To be honest, I think the proper way to use the Primetime Anytime feature would be to have it on or off and just leave it that way. Leaving it on will only take up one satellite tuner during the overnight hours and it won't take any hard drive space away from you to use. Turning it on one day and off the next is tedious and might even mess up your other series timers you already have set for other shows.
In whgdish's situation, just leave it on. If a sporting even comes up on ESPN he wants to see live, he'll have two tuners to still see it. If he starts making individual series timers for shows on the big four that share the same or have overlapping time slots, the box might not let him watch what he wants to see live because he'll run out of tuners. OR get an OTA tuner and an antenna.
Listen I know we are the tech savvy tinkerers and we just love to over do it just so that we have control and everything works exactly down to the letter like we want it too (it drives our wives if we have them crazy)... but in this case. So the software in the box work it's magic.