If you're firm with those dates - yep - planned is in order.
The gas station is 99% odds a 24-hour unmanned credit card operation though I would call a day or two in advance to ensure it's open and has fuel.
Operation at those locations is questionable if water levels are low. Hite Marina, when I visited after the Maze trip, was well out of the water (nobody around the dock area or camp sites) but the gas station / convenience store were open.