12 to 14 hours for Vyvanse
and 8 to 10 for Concerta. Thats very close to all day coverage
and not necessary.
Second, they are of two different chemical classes. Concerta is a methylphenidate based medicine, while Vyvanse is an amphetamine based med. Usually you go to an amphetamine based because your methylphenidate is not working for you.
The only possible reason I can think of to take both would be to turn off your mind at night so you could go to sleep and stay asleep.