I just spunked all of my rares on dual lands. Please applaud my levels of self-control. Now that I did that, I must ask, when do they rotate out?

A mana base without a deck! Nice problem to have I guess. I would imagine rotation in line with standard so which set did the rare land come from. When that set rotated out so would the associated rare lands. SD

https://mtg.gamepedia.com/Dual_land

I'm also buying out the ones I'm still missing, but avoiding the ones with green (and ocasionally regretting it).

Checklands are ok, they're ixalan and dominaria. The others are gone in october if they don't get a reprint.

All lands, no spells

Next level strat

Pro tip : the dual colour piles from the NPE got one rare land of their colour combination

Yeah, I just noticed that in a thread on the arena forum. I'd advise people to unlock these before blowing any wildcards, especially for play-sets (for example RG gives you a banefire)

Do these quests only come once a day? I would've thought the deck quests would be something that pop up right as soon as you finish the one before.