I can shed some light on this - the plane will have to have test flights completed in order to finish up the C/D checks. This will happen before the aircraft is ever handed back to Baltia. It will be whoever Kalitta employs/contracts to do "in-flights" (maintenance test flights). They'll likely be local flights starting and ending at Willow Run.

My guess is the aircraft will fly a few times between the time it is complete and when it's handed back to Baltia. Aircraft maintenance of that magnitude normally requires a few test flights to tweak everything the way it should be. Kind of like your mechanic driving your car around the block a few times to make sure it's back to normal before you go pick it up... only on a bigger scale.