Pe for life! Really I don’t know, but guess after you see gains keep on PEing for a few weeks and make sure the gains are still there, and are not just a post workout pump. After a few weeks of consistant size it is most likley cemented!
I’d add, at least a few weeks, possibly a few months.
"It's not the getting there but the going that's gotta be good." Varg
You just can’t see a gain and quit. You have to keep going for several weeks. Time at size is what will cement your gains.
It probably takes months to cement a gain, especially for girth.