Change the reset time to a fixed hour, instead of the hour you hit the sub button.
For instance:
You sub Jan 1st at 21:00. A month goes away. It's Feb 1st. You try to sub in the morning but you cant do it until 21:00. And that day you cant sub during night.

Just make it count on the day, so you can subscribe Jan 1st at 23:55, and then Feb 1st at 1:00