Factors that I can think of:
(a) how many frets being replaced.
(b) nickel or stainless steels frets being installed ... some luthiers take slightly longer with the later.
(c) amount of crowning done on the frets.
Could be a day .... could be slightly longer especially if the luthier has other work. Only person that can give you an accurate gauge is the person doing the refret job.