changing health insurance carriers -- overlap or allow gap ?

I am self-employed and provided my own health insurance through a "group-of-one" business plan. My wife just took a full-time job and it provides health insurance of equal or better coverage. I cancelled my business plan to accept coverage as a spouse under her insurance. However, the carrier informed me that this cancellation must be entered as of the 1st of the (any) month, and wanted to know if I wanted it cancelled as of the beginning of this month or next month. My wife's coverage began the 7th of this month. So, I can either have a 3-week overlap in coverage or a 7-day gap in coverage. The refund resulting from the latter choice would be significant. We required only an inexpensive ($28) prescription during that 7-day period, which I can have corrected (charged back to me).

Is there any down side to having a 7-day gap in coverage in order to get the refund, or must I accept the cost of the overlapped coverage? I know that there is a rule about not having a gap of more than 63 days to avoid pre-existing condition issues, but I don't know if there are any additional constraints that might bite me in the end if I cancel the policy as of the earlier date?