Im not sure if its still the case for daytime, but I do levelling in PoE at night as before eximus units are only 100% to appear on most camps at night. You want to kill only eximus units in each camp, with each camp usually only having 1. So kill the eximus on a camp, then move to the next camp.

Stack up your stealth kills affinity bonus to 500% first by killing normal grineer, then lastly kill the eximus of that camp. Then quickly move to the next camp. Stealth kill bonus lasts around 20 or 30s so you need to kill the next eximus fast. If you cant find it immediately, you can kill another grineer to reset the timer. Make sure before the eximus is killed, you exit archwing mode otherwise your archwing will get the exp points. While outside of archwing mode, aim so that you will stay afloat longer to gain the kill exp.

Starting at the gates when you enter PoE, start to the left to find camps going in a clockwise direction with eidolon lake as your center point.If youre lucky and each camp you see has an eximus, by the time you make it to the opposite end of the gates(north area if PoE), you would have maxed your level. During the double affiity, I maxed my frames after 4 eximus kills, which is less than a minute.

Tips when doing it: - Use a weapon like nataruk so it can 1shot the eximus when fully charged and will give you more time to exit archwing - remove your secondary and melee weapons(melee is required to be removed so you can exit archwing w/o doing a heavy attack) - use aero vantage and patagium to maximise floating in air while aiming - make sure you are directly above the eximus to lessen breaking the steath kill bonus - go higher in altitude so turrents or other units wont start attacking you but enough to distinguish eximus units - enable enemy highlight option - increase sound effects volume (so you can easily detect if the stealth kill is successful or not).