Make test timing fields explicit

tests/cmc-upgrade-kernel-test.md

@@ -171,7 +171,8 @@ Validate CMC behavior across staged kernel upgrades on a cloned VM, including re
 Use one cumulative results file and append one new section per tested host.
 
 ### Host Metadata
-- Test date/time (UTC):
+- Test start time (UTC):
+- Test end time (UTC):
 - Test duration:
 - Operator:
 - Source VM:
@@ -243,9 +244,14 @@ Also generate a run summary file in the same directory:
 Summary file requirements:
 - Start the file with the test file name line: `Test file: cmc-upgrade-kernel-test.md`
 - Title: `CMC Upgrade Kernel Test Summary`
-- Include UTC date/time for the run
-- Include total test duration for the run
+- Include test start time, test end time, and total test duration for the run
 - Include a short workflow summary (current kernel -> install CMC -> kernel upgrade -> uninstall CMC -> kernel upgrade -> install CMC)
 - Include host tested, kernel progression (start, step-up, latest), and overall result
 - Start each run section with a `##` heading that includes the OS family and the final outcome, for example: `## Amazon Linux 2023 - PASS`.
 - Put the OS version and the rest of the run details under that heading so the heading stays the visible OS label above the test snippet.
+
+### Duration Rule
+- Record the UTC start time when the run begins.
+- Record the UTC end time when the run reaches a terminal outcome and cleanup/reporting is complete.
+- Compute `Test duration` from the recorded start/end timestamps.
+- Backfill `Test duration` into the summary and results artifacts for any run where both timestamps are known.