I've noticed that rental cars are somewhat flexible in timings, you can be 2hrs late and the rates are still good.

If I have an existing rental with Alamo that starts at 7pm, is it pushing it too much if I want to pick it up at 7am, on the same day?

My reasons are that my travel plans have changed, and rebooking the itinerary will cause the price to go from $100+ to $200+