Between now and forever. AKA:
Soon™
Most likely within the next month... but could be a couple of months, depending upon how playtesting goes in both versions.
What
Stil996 said - the save file will work, but you will skip playing everything from v0.68 to v0.85.1 (2 updates plus a bugfix). You will still get the gallery.
However, for V0.82.4/v0.85.1, everyone had to start from the beginning because almost all the new content was in the beginning of the game because of revision writing and adding faux-sandbox events. So you might as well start from day 1.