As per the rEFIt main page, rEFIt is no longer under active development; however, a while back I forked off another project, rEFInd, which is being actively maintained. This type of change would require modifying the way the default_selection configuration keyword works by adding some way to specify different defaults based on the time. I doubt if this would be very difficult, although there would be documentation caveats concerning time zones. In any event, if you're willing to do some development, I recommend you look at the refind/config.c file and search for default_selection. That will at least tell you where the code would need to be changed. You should probably e-mail me (rodsmith@rodsbooks.com) to discuss how users should specify times.