Generally the guidelines are; one should wash after sleeping for at least half an hour, and at Alos hashachar (daybreak). So usually one sleeps overnight and wakes up after daybreak and you can wash according both those criteria.
But, on a journey, one should be aware of both these things. (It is probably advantageous therefore, to have an aisle seat, so you wouldn’t need to wake up your neighbour who may be asleep for hours when you’re hungry and can’t get out.)
**This reply should not be relied on, lease consult your local competent Halachic authority**