- give your body enough time to take advantage of the learning curve for an exercise to get an increase in poundage used and sustained adapitve response....
- However the first few weeks you usually will see the most progress with an exercise, also if you concentrate too long on 1 exercise (ed incline benchpress) you might lose some neurologic condition for the other exercise (eg flat benchpress)
So, do your flat benches for 3 weeks, long enough to make some significant progress with that particular exercise whilre short enough to retain most of your incline benchpress abillity etc...