Hi LarryMcJ,
You can absolutely keep trying, and spots do open up on occasion. People either remove themselves or we remove them if they become inactive. The difficulty with timing the latter is that even though we're doing that action in bulk, the spots aren't actually freed up until the latest build the individual installed expires. As such there is a fair bit of variability to it, and no real way for us to guarantee when spots will be open. I wish there were a better answer but if testing the EA is of interest to you I do think it is worth clicking the link periodically on the chance a spot happens to be open.
Ben