Actually -- through radiological study the Mean (average) time for gastric emptying of the stomach (in normal individuals) is 75% at 90 minutes. Complete emptying will occur at 90 minutes in some, and between 90 and 120 minutes in the rest (+ or - t1/2 avg). General anecdotal reports abound on the web give ranges from 1 hour to 6 hours as shown above.. often this is due to using unfounded generalities even on what appear to be reputable sites (IE: webmd, mayclinic, etc) -- For accurate information you need to look into radiological study's that are published by researchers and easily found.
With gastroparesis the individual is not considered normal as they have GI motility issues, and the gastric emptying is severely delayed, which coincidentally is where much of this 'overlap' of normal Gastric emptying timing references stem from.
If one has a gastric emptying time of 6 hours they need to be medically evaluated, it is not normal. If one has a gastric emptying time of less than one hour, they are not normal and need to be medically evaluated -- anything between 90mins to 180 mins compromise 99% of healthy individuals.
The stomach normally empties in 2 to 6 hours. However, many factors can speed up or delay the process. For example, some foods, diarrhea-causing bacteria, drugs and an overactive thyroid can hasten it, while an underactive thyroid and other drugs tend to slow it down. For more info visit www.mayoclinic.com/health/dumping-syndrome/DS00715 - Cached
Gastric emptying usually takes three hours in an average. Gastroparesis a condition which delays gastric emptying while dumping syndrome is a condition wherein a person digests and empty foods from the stomach very easily.