Numb finger question?

I'm left handed and I've been using scissors while working on a project and after a while of consistent use, my left thumb lost some feeling before I realized the scissors were right handed and that a groove in the thumb loop had been digging into my thumb and caused numbness through low circulation. I've switched to a pair of neutral scissor but it's been several hours since I lost feeling in my thumb and it's still numb and was wondering how long it could take for it to return? And how long before I should begin to worry it hasn't returned?