describing Voting once per day:

After voting, you'll have to wait exactly 24 hours (or the days interval entered in the backend * 24) before you can vote again.
So, if someone voted in the evening and then tried again in the morning, the system won't allow it.

If users are logged in, then their votes will be registered by the user id.
If the users are not logged in, then their votes will be registered by their ip address.