First, know whether the options you have are Friday a.m. or p.m. settled. There are some SPX options that do settle on Friday p.m. (The same goes with RUT and NDX; know your settlement date and time).
Secondly, attempt to avoid taking the setup "down to the wire." Ideally, you should be attempting to either close options setups out in profit with 4-10 DTE or look to roll a tested side or a side that is "too close for comfort" out for duration in this time frame. (In this particular case, I'm waiting to take this iron condor off until the last minute because I think price is going to be pinned here around 2090 running into Brexit).
Third, if you're absolutely set on taking the setup down to the wire, know your "drop dead" day and time and plan accordingly (I know I'm basically repeating myself here). For me, Thursday NY close is my "drop dead" date and time. I either have to shut the whole show down or roll something out before then ... . I won't be able to do it on Friday.
Good luck around Brexit, everyone!