With the hours you listed, we'd be looking at less than a year to upgrade.
If he's closer to 700 TT and willing to basically be TDY, it'd be even sooner - closer to 4 months.

We have two types of First Officers. Our EMB120 First Officers that we hire at 500 TT typically upgrade within a year. However, if they aren't willing/able to relocate and are on a lower-timed EMB120 route, then it will take longer. Our ACP First Officer that we hire at 750 TT typically upgrade within 4-6 months. They don't get assigned a base until they become Captains, because the goal is to get them to Captain mins asap.