Which tour legs can be dispatched?
For some tours, the legs must be flown in order. In that case, you will only be able to dispatch a tour leg if you've flown all previous legs in the tour.
You can see that this is the case on any Tour Details page. Note how the green Dispatch button is only available for leg 4, and not 5 or 6. This is because I have only flown the first 3 legs of this tour thus far.
Tours where the legs are not required to be flown in order will allow you to dispatch any leg at any time.
You may also dispatch any previously completed tour leg at any time, though this will not impact your tour progress in any way.
You can also dispatch a tour leg directly in smartCARS 3.