If there are standard time durations for the forms i.e. 1 month, 6 months etc. just have a created date that's automatically filled in every time you log someones overtime. While doing that, you can set the duration, lets use 1 month for example.
You can easily calculate the date that the entry needs to be reset, so you could just do something like:
If Date(this would be the system date) = ResetDate(this is the derived date based on the entry date + duration) Then selected fields = ""
Im using an access frame of mind for this problem, but if it was to work that way, you can easily adapt it to suit your needs.