But it's not as difficult as you say. Forget money. Just focus on the amount of weight loss you gained, and the amount of effort involved in minutes.
I'll bite one last time too.
This is an unimportant metric. Not only because the amount of time it takes has -zero- impact on the performance of the modification, but there will also be an absolutely unquantifiable difference in 'Time' based on factors, or a combination of factors, that you cannot possible measure or accurately reproduce.... tools, lighting, ambient temperature, mood, japanese assembly line torque wrench calibration, skill level, bike mileage, prior maintenance, make/model/year, music playing in the backround, beer consumed in the prior evening, beer consumed during
... the list is damn near infinite. What can take me 5 minutes can take some an hour. What I spend 30 minutes on some do in 5. The deviation is unpredictable & huge. It's just not accurate enough to reproduce, and 'estimation' is just an exercise in 'Large Window of Error'.
...and on the subject of 'Error': the job takes as long as it takes. None of these jobs take more than a few hours for just about anyone to do, but getting them done any faster will not yield better results. The 'effort' is irrelevant... you either do the thing to lose weight or you do not.... none of these things are so difficult that the deciding do/don't do factor will be effort. Maybe if you had 100 hours of work to do, and 80 hours to do it in could I see a need for organization like this... but you do not. No one here will either, and you will not get any good data as a result.
Frankly, a Time Vs Weight chart is pedantic and an outright waste of what you're attempting to measure. If you want to do it any way, slap the Easy Button and just look up the flat rate labor totals for each job and stick a weight value on it. Excel would do nicely for organization. It will be a neat but a passing curiosity that gets completely forgotten before the next model release, at best.