OK, I get that title may be a little more vague than I would like, but not really sure how else to phrase it. What my question really is, is can I put a 10-speed cassette on a hub that originally had an 8-speed cassette?

I have a spare set of rims and I'm thinking of setting up that wheel set for my TT bike. The TT bike is 2x10 and the spare rear wheel I have originally had an 8-speed cassette. What I want to do is have one set of wheels for my TT bike that are mostly for flat ground and then a second set with gears that are more for hills. So if I get a Shimano or SRAM 10-speed cassette, will it fit on the same hub as the 8-speed? Or is there a difference in the length or depth of the hubs between 8-speed and 10-speed?