Or, as the case may be, year.
If you had a chance to relive a day/week/month/year over and over again, where you didn’t age (except as normal throughout that time span) but yet you retained all of your memories, would you? And which would it be in particular?
As an added catch, you must declare, at the beginning, how long you want to relive this time period before time carries on as normal. This could take the form of requiring a specific action be done (i.e- I discover the cure for cancer).