more or less what I intended to do. Edit: it's kinda funny how we (I?) have kinda derailed this topic... lol.
For blutricity, battery boxes can be powered with redstone to prevent discharge. For Buildcraft, the energy link can be toggled with a redstone signal as well as the power switch pipe. So, all you'd really need is dedicated trade-o-mats to every customer and when they'd use the trade-o-mat, that could trip a logic circuit that could supply said customer power for an X amount of time.
perhaps. what we really would have to worry about at that point is how the time is measured, and if the server were to go down for some reason, then the circuit would most likely have to be reset. Also, we'd have to make sure to put down chunk loaders.
Unfortunately, I can't upload a screenshot or the program because my laptop's wireless card needs to be re-seeded but this is what I've ended up doing in a creative world as a POC. I setup a Trade-O-Mat and set it so when you put in 4 IC Credit, it'll give 1 paper. Then, from there, it'll emit redstone signal(s), dependant on how much IC Credits you put in at once which then goes to a Forth computer basically programmed to count redstone pulses and whenever it receives a redstone pulse, add-on 240 to a variable, X which will count down by 1 every second. If X = 0 then emit a magenta signal to an eu-splitter cable which will cut the IC2 power, coming from a CompactSolar MV, going to the client, and stop emitting an orange signal connected to another eu-splitter cable, connected to an MFSU for the MV power to bleed into when not providing power for a client. If X > 0 then cut the magenta signal and emit the orange signal so the power doesn't bleed into the MFSU. This setup is assuming that your world is day eternally, or you have a modded version of CompactSolars, which allows it to run constantly. Of course, I'm just making stuff up and tiffy probably won't even consider this setup as I'm assuming that she wants something more like a stop-n-shop instead of an electric company that requires client registry.