That had me thinking, if the version in Mania is the past version, does most of Sonic CD takes place in the future? Or will there be time travel in Mania for that stage's gimmick? And how did they get there in the first place, isn't SS on Little Planet?
Mania could take place before Sonic CD, in the part of the elevator when sonic chooses a button, you can see that the buttons represent the previous games (except the M, which represents Sonic Mania)
1, 2, 3, K, M
Sonic 1, Sonic 2, Sonic 3, Sonic & Knuckles, Sonic Mania