The delivery time I am uncertain about, could take from 2-3 days to in the worst case 1-2 weeks, but I surely hope Pimax did not try to save cost on that. Another problematic element in that could be customs clearance - hope the M1 don‘t get stuck with the customs and take ages to be cleared by paying VAT or whatever.
On the testing, I would expect the testers to take say 3-4 days to do first thorough testing, then report their initial findings to Pimax & the closed beta forum. Then they would discuss any issues, and possible fixes, work-arounds may be provided, so the testers can redo the test to get better results. I see this whole process to take 2 weeks, if relatively straight-forward. If it is not though, i.e. a not so small number of issues (even if not really critical ones), then this process may drag out. For how long ? Well, your guess is as good as my guess. So my estimation for us getting feedback is roughly 3 weeks from now, if everything plays out rather well.