Hi Sierrasmom,
it really doesn't matter how big/small or indifferent your pool is, whether your filter is black green red or blue, you backwash until your water coming out is clean/clear. Like Kurt mentioned, if you have a sight glass, it will tell you when to stop by the color (or lkack thereof)of the water, after stopping the pump, switch to rinse for about 10-20 seconds to clear out any debris still floating in the top of the filter.
If you do not have a sightglass, look at what's coming out the end of the hose - same deal there.
If your filter was extremely dirty, it may take 2 minutes or more to get it clean, if it was just somewhat dirty, a minute may do the job - see how pool size doesn't come into effect.