I see what you're saying NJE with regards to not knowing actual delay times. What I was proposing was rather more of an average value I suppose. For example, barring any major issues, I know that from engine start to take-off clearance, it takes somewhere between 10-15 minutes and on return its about 5 minutes taxi back to the apron
Currently I have an excel spreadsheet that I use, as I found a need to be able to compare aircraft costs vs flying time, of which that extra 15-20 minutes of hire time can make a considerable difference
It just occurred to me when I saw the costs calculated on the right-hand window based on the details entered into the aircraft details section for fuel costs/consumption