Can anyone clarify me something about Titan crystals please

Darkraw346

So there will be groups right? How does it work? One group at a time will be the pool or as time goes more champions groups will enter the pool so let's say a group contains 6 champs, at first the Titan crystals will contain only 6 champs (group 1) then after some time-12 champs (groups 1 and 2) and then 18 champs (3 groups) or what?
In short-i want 7* Kindred who will be in group 3 so I wanna understand how it works

Pikolu

18 champions in the pool and they get cycled in and out in groups of 6