One of the things of being on an european time zone is that when an american assumes that he's going to write you in the morning, it actually does it just after lunch :)
Joke aside, it would be awesome for this to have two things:
1) The ability to set a delivery hour
2) The ability to not receive emails on weekends
Apart from that, it's an interesting way to apply spaced repetition / exposure to knowledge.
I thought this too. It might be interesting to look at how many people changed the starting date to Monday instead of the default of tomorrow / Sunday.
First good habit: not having spam I react to in my inbox every morning.