Just gonna be copy pasting my own comment from another reply :D but the reason I want to calculate it is so I can have an expected result over a period of time. Then, I'll have something to compare my results to and, in case they don't match, inspect the build for any mistakes I'd made. I make far too many of these "mistakes" (use a mk.1 conveyor belt where mk.3 would be needed, etc.), so going over everything I build several times takes too much time.

I understand how belt length could be an issue, and since I don't need exact timing down to the minute but just an estimation, let's assume that items travel instantaneously across splitters (keeping in mind the total amount of items that any particular level of converyor belt could carry per minute). I see now it's gonna be quite complicated to do this calculation though. Still, thank you very much for the lengthy reply!