Hi orientfan,
Sorry to hear about your travails with this puzzle.
I do have a numerate (statistics) background but like you found the preamble well...daunting.
Key is getting the values of DURATIONS ( 1 to 9) in place. So that part is what I would call a 'conventional' numerical puzzle. These will give you 4-digit answers to the clue formulae.
For the grid entries, these answers are EITHER as BCEF values, ( so, e.g. 8923 would be 8=B, 9=C ,2=E 3=F) which you have to convert to a G value for entry OR they are G values that you have to convert back to a BCEF. You just need to do a bit of simple algebra to derive G in terms of B,C, E and F (and vice-versa), using the formula/expression given at the start of the preamble.
Hope this helps, it's worth persevering.