Every day. Since Gem Gacha floods me in R and SR fodder garbage every day and all my weapons are leveled up.
I'll soon run out of SR books to get stuff to level up, though. Then I'll need to sell that garbage for a whopping 10 Gems each...Oh, holy shit. I thought Sol was just bugged. But this makes sense.What Cobble said. Miracle Tickets pop-up about once every four months. We are... two months away from the next one? Ish? Are we? Not sure. Details!
Also, the guaranteed SSR gachas refresh about once a month, and Nutaku gives you a ~24 hour-ish warning about the refresh. We're about two weeks away from the refresh, I hope that they'll refresh it during Mammon.