Not maths as such, more precisely pseudomaths:
endhour == 23
starthour == 7
uploadpayload == 24
dayspermonth == 30
bandwidthused == (( endhour - starthour ) - 1 ) * uploadpayload * dayspermonth
bandwidthused = Oopsie!
Miscalculating the amount of data I was uploading to my web host would have totalled 6 times my monthly bandwidth allowance. As it happens it was lucky I caught it early; the 24MB included an early version of the entire folder contents I expected to upload - off by three times my expectation!
Felling silly.
Fixed? Well, I temporarily stopped the uploads prior to changing the routine to run every 3 hours - which may still exceed the allocation but I'm betting on…
I hope I can figure out how to transfer only changes to my site repo. I'll really need to closely monitor my sh\*t.