I am testing the 2005-04-23 experimental build (binaries from the OpenWrt site, not self-compiled) and I have just found that the ntpclient init script still has the same bug as in the older experimental versions.
When the WRT is not connected to internet, ntpclient cannot resolve the ntp server's name, and locks the boot process until it times out (or until I connect the WAN cable). Simply adding an "&" in the /etc/init.d/S41ntpclient script allows for the boot process to complete even if the WAN interface is disconnected, still ntpclient starts and when WAN is connected the clock is set correctly.
I don't know how to (and if I can) submit a patch to the CVS repository.