Check in times are set by the airlines. All bags now have to be TSA screened so airlines have added some time for screening. At most that adds about 15 minutes. Most airlines require you to check in 90 minutes prior for a international flight because a positive bag match is required. That means once your bag is checked the aircraft can't depart until you are onboard regardless of how long it takes for customs and security. Domestic varies by station but is usually 45 minutes with bags and 30 without.