diff --git a/lib/api/api.js b/lib/api/api.js
index 195441c3fe..349c29fc97 100644
--- a/lib/api/api.js
+++ b/lib/api/api.js
@@ -263,6 +263,19 @@ const api = {
                     request.serverAccessLog.analyticsUserName    = authNames.userName;
                 }
                 if (apiMethod === 'objectPut' || apiMethod === 'objectPutPart') {
+                    const setStartTurnAroundTime = () => {
+                        if (request.serverAccessLog) {
+                            request.serverAccessLog.startTurnAroundTime = process.hrtime.bigint();
+                        }
+                    };
+                    // For 0-byte uploads, downstream handlers do not consume
+                    // the request stream, so 'end' never fires. Set
+                    // startTurnAroundTime synchronously in that case.
+                    if (request.headers['content-length'] === '0') {
+                        setStartTurnAroundTime();
+                    } else {
+                        request.on('end', setStartTurnAroundTime);
+                    }
                     return next(null, userInfo, authorizationResults, streamingV4Params, infos);
                 }
                 // issue 100 Continue to the client
diff --git a/lib/utilities/serverAccessLogger.js b/lib/utilities/serverAccessLogger.js
index e6869df940..680dab63aa 100644
--- a/lib/utilities/serverAccessLogger.js
+++ b/lib/utilities/serverAccessLogger.js
@@ -320,16 +320,21 @@ function getOperation(req) {
     return `REST.${req.method}.${resourceType}`;
 }
 
+const assumedRoleArnRegex = /^arn:aws:sts::[0-9]{12}:assumed-role\/\S+$/;
+
 function getRequester(authInfo) {
     const requester = null;
     if (authInfo) {
+        const arn = authInfo.getArn ? authInfo.getArn() : null;
         if (authInfo.isRequesterPublicUser && authInfo.isRequesterPublicUser()) {
             return requester; // Unauthenticated requests
+        } else if (arn && assumedRoleArnRegex.test(arn)) {
+            return arn;
         } else if (authInfo.isRequesterAnIAMUser && authInfo.isRequesterAnIAMUser()) {
-            // IAM user: include IAM user name and account
-            const iamUserName = authInfo.getIAMdisplayName ? authInfo.getIAMdisplayName() : '';
-            const accountName = authInfo.getAccountDisplayName ? authInfo.getAccountDisplayName() : '';
-            return iamUserName && accountName ? `${iamUserName}:${accountName}` : authInfo.getCanonicalID();
+            // IAM user: emit the IAM ARN (arn:aws:iam::<accountId>:user/<userName>)
+            // to match the AWS S3 server access log format. Fall back to the
+            // canonical ID if the ARN is unexpectedly absent.
+            return arn || authInfo.getCanonicalID();
         } else if (authInfo.getCanonicalID) {
             // Regular user: canonical user ID
             return authInfo.getCanonicalID();
diff --git a/package.json b/package.json
index 90d7f1fb54..8feca11c8c 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@zenko/cloudserver",
-  "version": "9.2.24-1",
+  "version": "9.2.24-2",
   "description": "Zenko CloudServer, an open-source Node.js implementation of a server handling the Amazon S3 protocol",
   "main": "index.js",
   "engines": {
diff --git a/tests/unit/api/api.js b/tests/unit/api/api.js
index 78626bd651..9d08d33207 100644
--- a/tests/unit/api/api.js
+++ b/tests/unit/api/api.js
@@ -115,6 +115,40 @@ describe('api.callApiMethod', () => {
         api.callApiMethod('multipartDelete', request, response, log);
     });
 
+    ['objectPut', 'objectPutPart'].forEach(method => {
+        it(`should set startTurnAroundTime on request end for ${method}`, done => {
+            sandbox.stub(api, method).callsFake(
+                (userInfo, _request, streamingV4Params, _log, cb) => {
+                    request.on('end', () => {
+                        assert.strictEqual(typeof request.serverAccessLog.startTurnAroundTime, 'bigint');
+                        cb();
+                    });
+                    request.resume();
+                });
+            request.objectKey = 'testobject';
+            request.serverAccessLog = {};
+            api.callApiMethod(method, request, response, log, err => {
+                assert.ifError(err);
+                done();
+            });
+        });
+
+        it(`should set startTurnAroundTime synchronously for 0-byte ${method}`, done => {
+            sandbox.stub(api, method).callsFake(
+                (userInfo, _request, streamingV4Params, _log, cb) => {
+                    assert.strictEqual(typeof request.serverAccessLog.startTurnAroundTime, 'bigint');
+                    cb();
+                });
+            request.objectKey = 'testobject';
+            request.serverAccessLog = {};
+            request.headers = Object.assign({}, request.headers, { 'content-length': '0' });
+            api.callApiMethod(method, request, response, log, err => {
+                assert.ifError(err);
+                done();
+            });
+        });
+    });
+
     describe('MD5 checksum validation', () => {
         const methodsWithChecksumValidation = [
             'bucketPutACL',
diff --git a/tests/unit/utils/serverAccessLogger.js b/tests/unit/utils/serverAccessLogger.js
index a3c3c59d18..6f02034416 100644
--- a/tests/unit/utils/serverAccessLogger.js
+++ b/tests/unit/utils/serverAccessLogger.js
@@ -269,30 +269,41 @@ describe('serverAccessLogger utility functions', () => {
             assert.strictEqual(result, null);
         });
 
-        it('should return IAM user name with account for IAM user', () => {
+        it('should return IAM ARN for IAM user', () => {
+            const arn = 'arn:aws:iam::123456789012:user/myuser';
             const authInfo = {
                 isRequesterPublicUser: () => false,
                 isRequesterAnIAMUser: () => true,
-                getIAMdisplayName: () => 'iamUser',
-                getAccountDisplayName: () => 'accountName',
+                getArn: () => arn,
                 getCanonicalID: () => 'canonicalID123',
             };
             const result = getRequester(authInfo);
-            assert.strictEqual(result, 'iamUser:accountName');
+            assert.strictEqual(result, arn);
         });
 
-        it('should return canonical ID for IAM user if display names are missing', () => {
+        it('should fall back to canonical ID for IAM user when ARN is missing', () => {
             const authInfo = {
                 isRequesterPublicUser: () => false,
                 isRequesterAnIAMUser: () => true,
-                getIAMdisplayName: () => '',
-                getAccountDisplayName: () => 'accountName',
+                getArn: () => undefined,
                 getCanonicalID: () => 'canonicalID123',
             };
             const result = getRequester(authInfo);
             assert.strictEqual(result, 'canonicalID123');
         });
 
+        it('should return ARN for assumed-role session user', () => {
+            const arn = 'arn:aws:sts::123456789012:assumed-role/lifecycle-role/backbeat-lifecycle';
+            const authInfo = {
+                isRequesterPublicUser: () => false,
+                isRequesterAnIAMUser: () => false,
+                getArn: () => arn,
+                getCanonicalID: () => 'canonicalID789',
+            };
+            const result = getRequester(authInfo);
+            assert.strictEqual(result, arn);
+        });
+
         it('should return canonical ID for regular user', () => {
             const authInfo = {
                 isRequesterPublicUser: () => false,