one at a time

Sorry if this is a silly question - I've just started using Drupal last year and this is my first major upgrade.

I've got all my sites in one multi-site setup.

A couple of them are very simple, and basically good to go.

Can I upgrade just one of two of them at a time?

e.g. Could I create a new dir for drupal 7 and copy the sites over into it one at a time? (To eventually migrate all of them as the modules I need become available?)

FYI:

http://lx1.co.nz
http://nzmagic.co.nz

vs

http://amdramreview.co.nz
http://skeptember.com