They vary enormously. Our GOS gilt had 12 piglets in under two hours on Monday, with a pause followed by a fair bit of puffing in the middle when we suspect the last piglet from one horn of the uterus coincided with the first from the other, as one piglet eventually shot out so fast it banged its nose on the wall, followed 30 seconds later by a second one. Have you seen any afterbirth? Have you had any other litters sired by that boar? She may just have a very small litter.