After some trial and error, I think I found a solution for my specific problem. In the old fstab, the address of my NAS did not end with a domain name of any kind. Now, it seems to be required that this address includes the .local as a domain. When I add .local to the nfs entries in fstab, then the shares are mounted correctly, and no wait occurs (as long as these are available - I have not yet tried to boot in their absence). I still think this should be considered a bug, since there is no reason why the system should wait such a long time (around 10 minutes). Instead, it should flag the absence of those shares and continue to boot the rest of the system.