I had to shift my flight time by a few hours last month because a meeting ran over, and it was surprisingly painless. The best way to do it is through the United app while you’re on the go.
I just pulled up my itinerary under "My Trips," tapped on "Change flight," and it let me browse other times for that same day. It was so easy to modify my departure to a later slot without having to wait on hold for a representative. I even managed to snag a window seat on the new flight!
Would you like me to see if there's a price difference for the specific flight time you're eyeing?