Duty Roulette: You have Low Level, High Level, and Main Scenario that give massive daily bonuses, and they take 25-30 minutes each. Do at least one or two a day.
I just wanna chime in and say the duty roulettes are 100% not worth it. All three only reward as much as a heavenward dungeon's clear EXP for completion - and unless you get a heavensward dungeon out of the low level roulette (unlikely), you're missing out on the oodles of EXP the mobs in those dungeons give you (esp bosses).