You could do one day In Frankfurt, but leaving the same day will ruin the visit, as was mentioned the clubs don't get busy until the evening. Best bet Is to book a room In a nearby hotel, and flight home the next morning.
Frankfurt Is a good choice, visiting Palace Is probably top of the list, for choice of girls, easy location In city centre, and hotel around the corner. Oase Is a bit of a trek out In the country for a one day trip.
Berlin could also be an Idea, world city with a lot to do tourist wise, only has the one fkk Artemis though.
Cologne, I know this city very well, If you can get a handy flight Into Cologne airport (Easyjet fly from Gatwick) then Samya Is only a U-bahn train ride away, a club well worth a visit, as my reports show, not as big a club as the others mentioned, bet still a lot of girls to choose from most days.