improve: duration for initial interval in GenericRetry #5494

Job	Run time
sample_operators_tests (sample-operators/leader-election)	3m 22s
sample_operators_tests (sample-operators/webpage)	3m 13s
sample_operators_tests (sample-operators/tomcat-operator)	2m 30s
sample_operators_tests (sample-operators/mysql-schema)	2m 38s
	11m 43s

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