Yes, you can marinate for too long. The acid in the marinade will start breaking down the meat, leaving you with a gritty or mushy texture.   Most recipes for marinating meat and poultry recommend from 6 hours up to 24 hours. It’s safe to keep the food in the marinade longer, but after two days the marinade will probably start to break down the fibers of the meat, causing it to become mushy.