Hi @LauraleeG
Alternatively, I think we can write an expression directly in SharePoint column to get this done. Please use the below expression for start & end time:

Expression used for Start time:
formatDatetime(triggerOutputs()?['body/start'],'yyyy-MM-ddTHH:mmZ')
Expression used for end time:
formatDatetime(triggerOutputs()?['body/end'],'yyyy-MM-ddTHH:mmZ')
I hope these expressions will resolve the problem.
If this helps & solves your problem, please remember to give a 👍 and accept my solution as it will help others in the future.