Allow 12 hour days
I would like to have the opportunity to review the cards I learned in the morning again in the evening. The simplest way to do that would be to allow a 12 hour day. That way scheduled cards come up every 12 hours instead of when a new day comes.
See this proposal, which is more general:
Sharon Cash commented
You could have a toggle switch so only the people who like this option could use it. I like the idea of doing my cards in the morning before starting my day and again in the evening after work.
You can use Tags.
I don't think this is a good idea: all the research shows that sleep is very important in forming memories, which is why each new day starts in the morning.