Duh! Of course I know this. But you can create a Lv1 character and take it straight to town (talk to NPC) then talk to notice board. Which is besides the point.
Then get the chest (if not hard coded), because apparently it’s designed to take into account Lv1 ~ 49 growth. Hopefully that’s not the case.
From what I’ve observed, so long as you fall within the ranges mentioned above, the requirement is fixed.
Eg: Lv234 needs 3 levels to open their chest. They land at Lv237, they now need 2 levels to open their next chest.
I highly doubt IMC would design a system as complex as one that snapshots your current level when you obtain the Treasure Chest and goes on from there. Tiering is easier.