I hope I can make this make sense. I am sure the answer is very simple as
every spreadsheet that underpins a budget must allow for flexible forecasting.

I am trying to create a spreadsheet that allows me to start calculations
anywhere on a time line and allows me to change the amount of time that the
calculations will last. For example, if I am looking at a 12 month time line
(Jan to Dec) then I want to be able to start a function in any month and then
for that function to last for any amount of time. So the first function may
start in Jan and last for three months. In parallel a second function may
start in Jan and last for five months and then a third function may start in
Feb and last for two months.

How do I set up a sheet so that when a function starts, the sheet know to
mark each cell on the time line that relates to the amount of time that the
function will last.

Confused? I am...and therefore in need of help.