I think what you are trying to do is great.
I have to be honest here your going too fast!
No way will you get people to login every day life itself gets in the way
To start off I would try once a week and yes stretch your quiz over 7 days once you have people answering in a few days you can introduce a 2nd in a week then a 3rd if things hot up.
If you try too hard you will just frustrate yourself.
hope this helps
Izzy