How long has this been going on? If it has been only a few day, the animal is probably preparing to molt. If it has been longer, say over a week, then it is either finding other food in the aquarium, has damaged appendages that doesn't allow it to process the the food your are providing, is sick (disease or parasites), or it is just being contrary and doesn't like its dinner. (I'm not being factious! Some stomatopods develop food preferences and it can take them a couple of weeks to change their diet.)
About a week on average, but I've seen up to two weeks. My G. Ternatensis just molted. Took about 6 days total before he started taking food again. He was busy eating his molt for about two days, he did some house cleaning then started taking scallops again after a couple days.