Just my two cents...
When I had nuclear Gastroparesis testing, I sat up about a 30 degree angle and was given Oatmeal, since I do not like eggs. The whole test lasted about 2+ hours, with feedings and pictures taken at specific intervals. Even though I had a bit of reflux at that degee of recline, the test proved normal for me.
The radiologist was really great - she spoon fed me (certain amounts.) :)
The entire time for the test does depend if if have normal motility, hyper or hypo.
Once the last bit of food enters the Duodenum, the test is offically over.