How to let a loop run for a while before checking for break condition?

[Claudio Grondi]

Sometimes it is known in advance, that the time spent in a loop will be 
in order of minutes or even hours, so it makes sense to optimize each 
element in the loop to make it run faster.
One of instructions which can sure be optimized away is the check for 
the break condition, at least within the time where it is known that the 
loop will not reach it.

Any idea how to write such a loop?

e.g.

counter = 2*64

while counter(BUT DON'T CHECK IT THE FIRST ONE HOUR LONG):
   ... do something ... # and decrease the counter

Thanks for any hint, but in particular if related to timers on the 
Windows 2000/XP system I am mainly working with.

What do you think about this idea? Does it make sense?

Claudio Grondi