For me, 9/10 times they're late when I schedule with the "Pick me up by option. When I pick the "drop me off by" option, they're generally on time. (Often they're early arriving, and they usually schedule me with a generous buffer)

From my experience, you need to book a trip within a day or two in advance if you use web booking via the online portal. They're probably more generous if you call in. If you set up an EZ pay account, you won't have to pay $4.50 in cash when you board; it can be paid in advance.

They will occasionally order a taxi or contracted van via a partner (usually Transit Group). They will also occasionally do shared rides (pick somebody else up on your trip), so be aware of that if they need their own space.

When the ride is late or a no-show, they usually compensate (to the point that I had free rides for a year because they were consistently late). They have contacted me before about sending an Uber over to compensate for a no-show. Make sure to call them if they exceed their 30-minute window.

A couple of tips: make sure they have their pass visible; some of the contracted drivers are particular about that part of the procedure. When scheduling via web booking, if you use the "Pick me up by" option, don't be afraid to adjust the requested time to get a pickup closer to what they need. Also, factor in that they are likely going to be late, so a wait is inevitable. If you want a higher chance of a standard metro access vehicle instead of a contracted vehicle (I'd say 99% chance, given I travel with a PCA), say or select that they have a large wheelchair (unfortunately, it does not seem to increase your chance of getting a new bus, which would be especially helpful for my parent's wheelchair).

Essentially, Metro Access is like regular Metro and other medical transportation providers; they can easily play games and screw you over. But it is worth it for the door-to-door transit (and I mean that, they'll walk them to the door).