The website says $2 per 15 minutes with no mention of free period that I can see. That may not be a bad deal in itself if it does shave off some time getting there and avoiding having to drive the domestic terminal loop.

That said, I do remember entering the domestic garage once in the past year where I had to immediately exit (I chose the wrong entry gate for a prepaid booking; apparently only a limited number of them were equipped with QR code readers at the time) and I wasn't charged using the same ticket that I pulled when entering. Although I was probably in the garage for less than 2 minutes then.

But if it is 10 minutes, that's more than enough time for a drop-off. Plenty of time for a pick-up as well, as long as the driver doesn't have to wait for passengers to arrive and/or wasted time trying to find meeting point.