imo it should be a one time thing.
One day, given a week in advance. One shot, and that's it.
Also add a qi restriction to it (101qi) to prevent abuse. So that people don't just alt farm against themselves, tc transfer e.t.c.
reason for 101qi if you don't know is because you can get 100qi a day so for those nerds who would actually go the effort of playing 100 games multiple times a day for a shot at double tc.