On the last day of a MULTI day trip (2,3,4 days) - the earliest your reassignable can start is 6am (you dont have to answer your phone beofre that) and you have to sign off no later than 2 hour after your original sign off.
Earlier reassignable spans would only apply to intermediate days (ie days 2,3 of a 4 day trip).
more often they will give you an airport when you call to clear yourself - that we they've got you at the airport at 6.