If you need two coats, it's because the asphalt's extremely porous, gray, and aged, at which point, we'd recommend applying one coat of sealer, letting it dry over 24 hours, and then applying a second coat. That way, you're sure to put down a proper application of sealer, protecting that asphalt investment.
Seal coating takes a little bit of practice, but once you've got it down after a few hours, it's really easy to do.