If you are on daily PrEP, then ... every day. Research shows it takes about 7 days or so for the anal tissue to have the maximum protection from daily PrEP.
Alternatively, there is also PrEP on Demand. You can read more: https://www1.nyc.gov/assets/doh/downloads/pdf/ah/prep-on-demand-dosing-guidance.pdf
You can't do both PrEP and PEP at the same time. PEP also has Truvada or Descovy as one of the regimen so you can't do both at the same time (plus if you are correctly dosing on PrEP, you wouldn't need PEP anyway)
If you need PEP, ASAP is the correct answer but in any case, no more than 48-72 hours after the sexual encounter.
There are only 3 PrEP approved: Truvada, Descovy and Apretude. The last is the newest, and is a depot injection that will last about 2 months (after initially with the pill trial to ensure tolerance).
PEP formulary will be based on what is approved in your jurisdiction. You don't have a choice in that regard.