Then the minimum day provision applies. Any time you report for duty it's a 4 hour minimum pay day.

Lets say that you do 2 flights SAT times of 1.5 and 2 hours. That will be 3.5 hours, thus the min day provision applies

Now let's add a third flight with a SAT time of 1.0. Now it's 4.5 hours pay. Let's say you underblock all the flights by 20 min each, it won't matter because you still get paid at least the SAT times.