you want to stay near the 3 second mark on the bench. what you want to do, as i see, is take the same time to complete all 3 benches or both squats as it takes you to lift your max. i don't really think this happens that often. if you watch the westside guys lift in a meet, they fast throughout all their reps.
if you're not under 3 seconds on the bench then it is probably too heavy.