Is a wedding that's being held on 09/25 at 7:30 pm outside formal?
This depends on the exact setting, whether tents have been set up or if a temporary shelter has been put up. If you have the invitation, it should be indicated at the end whether the wedding is formal or not.
Depends on where outside. I have seen many formal ones with tents a and floors put down. I have also seen a lot less formal ones. (BTW bug spray and pantyhose don't mix. It melts the hose.)