It totally depends on your prescription. If there’s no astigmatism, the lenses can be stocked and cut to the frames you need. Astigmatism adds another two variables that make it much harder to stock. Also the stronger your prescription, the more alternative material options there are to keep the thickness down, which again makes it harder to stock everything.
Most offices who keep stock lenses keep cyl (astigmatic correction) up to two diopters in quarter increments in my experience.
The main limitation is usually material choice.
in the Boston area it is typical, several choices to bring your script and have new glasses in an hour or two, i have used lencrafters for 10 years like this
Wow, that's awesome. I've never been able to get glasses in less than two weeks. Last time I went to Lenscrafters was 20 years ago, I guess they have changed a lot since then.