Short answer is yes. In the start field simply type in the date and time.
Format is (using your example and assuming you have the options set to show
dates as mm/dd/yy) 02/19/08 3:00 p.m.
Word of caution though it is not a good idea in general, to fix start times,
unless it is the first task in the project, or you simply do not want it to
start any earlier, and will not start earlier. It is surprising how many
times I find first guesses at when something can start, and it ends up
starting earlier.
hope this helps
Regards
DavidC