you can veg a plant indefinitely. typically its about a month or two unless its an autoflower. for the most part its all about your environmental restrictions sorta.
it also depends on the strain. some take longer than others. if its your first go around sit back and enjoy the show. if nothing else you will have learned something about your plants.
basically i let mine get to about half the height of the room...ish (24 -36 inches maybe depending on strain?) and switch them over.
when grew outside i would start my plants in the middle april and get them outside by maybe first week of may at the latest.
they didnt get yanked until the middle or end of october. thats a good 6 months of grow time, 3-4 months or so of that was veg time. my plants would get huge
8-9 foot tall and fat. thats really impractical indoors so the veg time gets cut shorter.