diff --git a/flaml/automl/time_series/ts_data.py b/flaml/automl/time_series/ts_data.py
index 239d02c3ba..4a650db71c 100644
--- a/flaml/automl/time_series/ts_data.py
+++ b/flaml/automl/time_series/ts_data.py
@@ -245,12 +245,13 @@ def prettify_prediction(self, y_pred: Union[pd.DataFrame, pd.Series, np.ndarray]
 
         else:
             if isinstance(y_pred, np.ndarray):
-                raise ValueError("Can't enrich np.ndarray as self.test_data is None")
+                y_pred = pd.DataFrame(data=y_pred, columns=self.target_names)
             elif isinstance(y_pred, pd.Series):
                 assert len(self.target_names) == 1, "Not enough columns in y_pred"
                 y_pred = pd.DataFrame({self.target_names[0]: y_pred})
-            # TODO auto-create the timestamps for the time column instead of throwing
-            raise NotImplementedError("Need a non-None test_data for this to work, for now")
+            if self.time_col not in y_pred.columns:
+                forward_frame = create_forward_frame(self.frequency, len(y_pred), self.end_date, self.time_col)
+                y_pred[self.time_col] = forward_frame[self.time_col].values
 
         assert isinstance(y_pred, pd.DataFrame)
         assert self.time_col in y_pred.columns
@@ -499,10 +500,18 @@ def fit_transform(self, X: Union[DataFrame, np.array], y):
 def create_forward_frame(
     frequency: str,
     steps: int,
-    test_end_date: datetime.datetime,
+    last_timestamp: datetime.datetime,
     time_col: str,
 ):
-    start_date = test_end_date + pd.Timedelta(1, frequency)
+    if frequency is None:
+        raise ValueError("frequency cannot be None")
+    if last_timestamp is None or pd.isna(last_timestamp):
+        raise ValueError(f"last_timestamp cannot be None or NaT, got {last_timestamp!r}")
+    try:
+        offset = pd.tseries.frequencies.to_offset(frequency)
+    except ValueError as e:
+        raise ValueError(f"Invalid frequency {frequency!r}; expected a pandas offset alias.") from e
+    start_date = last_timestamp + offset
     times = pd.date_range(
         start=start_date,
         periods=steps,
diff --git a/test/automl/test_ts_data.py b/test/automl/test_ts_data.py
new file mode 100644
index 0000000000..042eddedf3
--- /dev/null
+++ b/test/automl/test_ts_data.py
@@ -0,0 +1,63 @@
+import numpy as np
+import pandas as pd
+
+from flaml.automl.time_series.ts_data import TimeSeriesDataset, create_forward_frame
+
+
+def test_prettify_prediction_generates_timestamps_without_test_data():
+    train_data = pd.DataFrame(
+        {
+            "ds": pd.date_range("2020-01-01", periods=4, freq="D"),
+            "y": [1.0, 2.0, 3.0, 4.0],
+        }
+    )
+    dataset = TimeSeriesDataset(train_data, time_col="ds", target_names="y")
+    expected_times = pd.date_range("2020-01-05", periods=2, freq="D")
+
+    for y_pred in (
+        pd.DataFrame({"y": [5.0, 6.0]}, index=[10, 11]),
+        pd.Series([5.0, 6.0]),
+        np.array([5.0, 6.0]),
+    ):
+        prediction = dataset.prettify_prediction(y_pred)
+        assert isinstance(prediction, pd.DataFrame)
+        pd.testing.assert_series_equal(prediction["ds"], pd.Series(expected_times, name="ds"), check_index=False)
+        assert prediction["y"].tolist() == [5.0, 6.0]
+
+
+def test_prettify_prediction_generates_monthly_timestamps_without_test_data():
+    train_data = pd.DataFrame(
+        {
+            "ds": pd.date_range("2020-01-01", periods=4, freq="MS"),
+            "y": [1.0, 2.0, 3.0, 4.0],
+        }
+    )
+    dataset = TimeSeriesDataset(train_data, time_col="ds", target_names="y")
+
+    prediction = dataset.prettify_prediction(pd.DataFrame({"y": [5.0, 6.0]}))
+
+    pd.testing.assert_series_equal(
+        prediction["ds"],
+        pd.Series(pd.date_range("2020-05-01", periods=2, freq="MS"), name="ds"),
+        check_index=False,
+    )
+    assert prediction["y"].tolist() == [5.0, 6.0]
+
+
+def test_create_forward_frame_uses_next_frequency_offset():
+    # Pandas 3 uses QE-DEC while older supported versions use Q-DEC.
+    quarter_end_freq = "QE-DEC"
+    try:
+        pd.tseries.frequencies.to_offset(quarter_end_freq)
+    except ValueError:
+        quarter_end_freq = "Q-DEC"
+
+    weekly_frame = create_forward_frame("W-SUN", 2, pd.Timestamp("2020-01-05"), "ds")
+    quarterly_frame = create_forward_frame(quarter_end_freq, 2, pd.Timestamp("2020-03-31"), "ds")
+
+    pd.testing.assert_series_equal(
+        weekly_frame["ds"], pd.Series(pd.date_range("2020-01-12", periods=2, freq="W-SUN"), name="ds")
+    )
+    pd.testing.assert_series_equal(
+        quarterly_frame["ds"], pd.Series(pd.date_range("2020-06-30", periods=2, freq=quarter_end_freq), name="ds")
+    )