Do this before using the "chill session-method" with the last character for eventually "Time Traveller CHAMPION!" Using the chill session method with ALL character will make this achievement unobtainable.
Collect 50 leaves in another run to unlock Checkpoint Challenge. Then choose Checkpoint Challenge, pick a character and finish the run. Collect leaves to add seconds to the timer and the checkpoints give you +25 seconds. The fifth checkpoint is the finish line, at the end of the autumn stage (red, brown, orange, yellow color pallet). Estimated time to complete is about 15 minutes and you are allowed to spend clips for a continue (first continue is 400 clips and second continue is 800 clips). Collect clips with picking up acorns, doing the jumps and tricks and hitting the owls.
For me this achievement didn't unlock, as I already did the "chill session-method" which each character for Time Traveller Champion. After deleting save you have to collect the 50 leaves again to unlock Checkpoint Challenge. First run after deleting my save (local and from the cloud), did unlock the achievement for me with Jessie. Have to beat the whole game again (full sticker board,, 5 acorns, 15 feathers etc. Not that I don't mind it, I think it is enjoyable) for Platinum Player.
Edit 23/02/2018: According to cccxDOTbelieve above matter is fixed, I cannot confirm this.