Of course, it also depends on the WU (work unit).
Those without gaussians (bell-curve signals) are obviously going to go through processing superfast, and those with loud noise are going to be processed even faster, often within a few minutes before getting another WU.
Remember: it's doing all these calculations over a range of doppler shift values, and all that math takes time. Those running the program as a strict screen-saver will wait an eternity for just one WU to process, even though the total processor time for one will amount to a few hours. Running it overnight as a standalone program is the only way to go.
Which, BTW, is how I'm up to 777 WU's processed -- since the program started back in '99.