not much work in the beginning.
The problem born when you want to move one flight to a bigger airplane but then when this new plane has free time you cannot insert the flight because you have another one at the same time!
So, all theese problem I have with routes lasting 4:00 hours more or less, and it is not possible to differentiate starting time, not go under 5:0 am and over 23 pm and still have the chance to makje 4 flights a day.
Unfortunately where I need a321 I do not have enough request on shorter routes to mix them and reach 4 flights a day!