P-chan, there are always more hairs than you'd think, since only a third of your hairs are visible at any given time.
If you go in regularly for an hour or two a week, you should be able to get most of the dark hairs gone pretty quickly. It's hard to predict, since there are a lot of variables.
Once they've been cleared, you will have dormant hairs come up, and you'll also have some regrowth.
Your best bet is to have a consultation, where they can give you a better sense of what to expect. If you don't have a lot of hair, it might take 30-50 hours total over a year or two. If there's more than you estimate, it might take longer than that. A normal male beard wll usually take 100-200 hours to get every single coarse hair. Many men don't want to get all of it, just the dark ones, so it may be less. Some men with light skin and dark hair have had a few laser treatments followed by electrolysis, but there's not much information on how much time this might save.