BBM: It could also mean he was at the rest area for X time, went into Buttonwillow proper for X time (possibly in the motel parking lot or truck stop) then got gas when he was ready to leave if he only went to the exit near Lagoon Drive (where the Shell station is on the corner of Tracy and Lagoon). Just because he got gas later in the day, it does not mean he stayed all day at the rest area.
BBM - True, but according to our holey timeline, we don't have any information/indication that he was anywhere other than the rest stop from the time he ran out of gas until he was next located by CHP during the wellness check at 9pm or 9:33pm "at a hotel" at Hwy 58 and Fwy 5 in Buttonwillow.
ETA: Besides, of course, the 2nd roadside service check which also places him at the rest stop, in the same spot, sometime "several hours after" the 12pm gas delievery.