It would be wonderful to stay open 24/7 but this would also mean that someone is available to assist clients which in not always possible.
By setting business hour you provide yourself to close and prepare for the next day so you are refreshed and energized for the next day of work. A few things to consider would be to let clients know that there could be a wait time before login credential are send 12 hours should be plenty of time but processing them faster is always a plus. This is for two reasons it will allow you to catch-up from any late night purchased and it could possibly eliminate responding to multiple email stating "I purchased service were is my login information", this will only slow the process down if you have many email to answer.