I have 5 kegs I want to carb with a single co2 tank, I have a splitter, but I don't know if I need to apply the same amount of pressure I apply to a single keg, I carb using the 40 20 method, which is 40 psi for 24 hours, then 20 psi for another 24 hours and finally at serving pressure, will I get the same results if I apply it to five kegs at the same time?
Yes, use the same pressure as for one keg. You can do this and it will work as expected I do it often - I have a primary regulator, 4 x secondary regulators, and each secondary feeds a 3 or 4 way manifold. The fact that you are using a pressure regulator means that all kegs will be kept at the same pressure and will not overshoot or have any other problems. There is no difference between carbing one keg or 5 you use the same pressure, but of course, you use a larger quantity of co2.
If you don't have a check valve on each line of your splitter, be sure not to fill the keg too much, so that the liquid level is below the gas dip tube, or you can end up pushing beer out into other kegs.
You should get the same results, though it will take longer for five kegs to come to the same pressure than for one (possibly minutes, rather than seconds).
The gas will flow from a location of high pressure to one of low pressure until it's all equalized. It doesn't matter whether that location is one keg or if it's distributed across one hundred of them. The only limiting factor is the amount of gas in the reservoir tank. If there's not enough gas in the tank to get all five kegs filled, then they'll all equalize out at some lower pressure.