It could take weeks, or even months before a VAC ban gets put into effect, In the case that you did use a detected hack and your account got flagged, I would give it A week or two to make sure that It wasn't detected. All in All, remember not to hack on your main account and buy a copy on another account if You're using public hacks.. It's safer that way.
EDIT : -- Unless you were hacking really obvious in MM or any other AR ect, In that case an over watch/untrusted ban can come really quick and soon.. These are essentially the same as vac bans now. (They used to be one year bans)