The best informed guestimate I can provide, going by the number of people who have posted here a couple days up to a couple weeks after stopping a medication thinking they have a post-drug syndrome and then never returning, would be a month.
There are quite a few people though who seem to begin experiencing significant recovery up to the 6-month mark and rarely, within the first year after stopping. I believe these are afflictees of a post-drug syndrome who are able to recover naturally somehow. The remainder of us, not so lucky.
What I am saying is that it is very likely that you will simply need to wait a few weeks for the immediate effects of the drug to wear off.