There's also no decay in provisional matches. You can only demote out of your division or tier if you lose while at zero LP. Demoting to a lower division or tier happens when your MMR is too low for your ranking, and you have zero LP.

How does decay in TFT work?

Everything you (probably) ever wanted to know about Decay:

In Master and above, you bank up to 10 games, with 1 banked game getting removed each day. Watch out! You lose 250 LP every day if you don't have a banked game to lose. As of patch 10.6, you cannot demote out of Master from decay.

How long does it take to decay TFT?

FYI there is decay in TFT ranked for diamond and above. Also you won't demote through tiers (like from Plat to Gold) unless your MMR is too low for your current ranking. In Diamond, you lose 50 LP after 30 days of inactivity, with -50 LP every seven days after that.