On the one hand, choosing an arbitrary but good enough target avoids wasting effort on overoptimization and ensures a focus on the worst case, not on the best case; on the other hand improvements are not elastic: maybe rearranging parts and supplies to make them more accessible is enough to make 28 minutes as likely as 30 before, but getting to 26 minutes could require expensive tools and 24 minutes would require different, easier to service aircraft.
Yup. Optimisation is always a trade-off problem that needs to be approached intelligently, not mindlessly. The raw metric of minutes to airborne leads naturally to the intelligent points you raise about what each minute is worth.
The arbitrary target implies a cost function that is infinite below 30 minutes, and zero above it – this, if anything, suppresses intelligent discussion and leads to wasted effort.
