XPS M2010 Raid Rebuild Time

I have an XPS M2010 (4 GB RAM) with two 250 GB, 5400 rpm HDs in Raid 1 configuration. I'm about to replace the HDs with two 500 GB 7200 rpm Seagate Momentus units.

I'll replace them one at a time and let the Raid controller rebuild the array. Does anyone know how long it is likely to take to do each rebuild? I need to make sure I don't get stuck in the middle of it at a time when I need to shut it down and move it. Also, during the rebuild, will the system still be usable as it is during a verify?

FYI, if I have to do a forced reboot now, it takes about 2-1/2 hours for the system to finish verifying the data, during which time I can still use it, though it's slow. Also, I have about 150 GB out of the 250 GB on the present system full.

Thanks in advance...