I would think that might depend on the stocking level and the amount used. Since fish are always secreting free ammonia, Prime will find those and bind to them. Although your ammonia test shows a high reading sometimes with Prime it is actually reading the converted safe ammonium levels so it will take several days for the free ammonia to get back up to toxic levels. This is my understanding and why I think it is probably unnecesssary to dose every 48 hours because that is the time it probably takes to break down in a "normal" tank. If your tank is uncycled and you have tons of free ammonia or chlorine in the water it may be neutralized at a much faster rate. So, really it probably depends on your tap water chlorine/ chloramine levels, the amount you dose, the period you are in your cycle, and your stocking level. They probably interact and why Prime is just a temporary band-aid to help correct water quality problems and why you can up the dosage depending on that. That may be why Prime is so good, it is so concentrated it is hard to screw things up and probably hard to under-dose your tank.
Whether its pointless to you or not it does not matter it is not your thread.