Hello Guys!,
I am just a little bit confused and also wants to know. If you schedule a flight then in the page there will be a time for arrival and Ready For Departure.
Now the question is, What does Ready For Departure mean?
It has already loaded the passengers on the flight? done turnaround times?
Thank you in advance for your answers!
´Ready For Departure´ means that the plane is ready to depart from that time on.
It may depart later, if you wish, do some maintanence first or wait for some transfer passengers,
but everthing that actually needs to be done, like unloading and loading passengers and/or cargo,
refuelling and whatever else there is to do, has been done.
Well, the “Ready for Departure” does not affect you or your airline, since there are no delays in AirlineSim. Just imagine it as pre-flight checks and tower communications crew has to do before departing 
Put quite simply, the "Ready for Departure" time is that time at which turnaround is completed. From that time onward, you can schedule the departure of the next flight.