That depends on the model. For a PowerPC-based system running the Mac
OS v9- S@h client/screensaver continuously with a blank screen, I'd
expect that kind of time (~ 1.0 day/WU) from a G3 running at 200-250
MHz, which I think is about right for the CPU in an earlyish iMac.
For a system that's also running other programs or gets shut down
occasionally, you have to prorate the figures accordingly: if the
statistic under discussion came from a machine in which the Mac
client was only actually crunching half the time, I'd guess it to be
a 400-MHz system.

Good detective reasoning! I have an iMac 400 MHz, 192mb ram   I don't
leave it on all the time, and when it is on its generally in use -
hence it completes a WU in about 14 hours.

My problem is - I don't really want to go OSX on this machine - so no
seti@home for me in a couple of months..