I usually only play one game at a time with login quests/dailies. Right now that's Legend of Solgard on mobile. There are login quests with a minor but important reward, a more substantial reward for logging in 7 days in a week, and daily quests that pay off with a different type of small reward each but give a bigger reward if you do them all.
It probably takes me an hour or so easy h day to do the daily quests. They basically revolve around doing one battle of each mode you've unlocked. It's totally worth it to do all of this anyways, because each mode has a focus on a different reward structure (some let you earn a lot of non-premium currency, some let you items for leveling up characters, etc). I really like the game, but the burden is so great that I usually spend whatever time I'm going to give the game on doing these quests instead of actually playing campaign levels.
And there's no way I could play 2 of these games at once. I don't mind a little motivation to play a f2p game, especially if they are letting me earn stuff they'd rather me spend cash on. But it's undeniable that these mechanics turn the games into a chore. When Animal Crossing comes out, I'll probably drop whatever dailies game I'm playing for that, due to it's similar sort of daily play system.