You can write as many diary posts that you want but you can only submit 1 entry per day.

If you want to write one for each of day of the week you can do so and if you only want to write 1 post for the week it will also count.
In the end it will be the 3 BEST diary post for the week that will be the winners and not the amount of posts that you have submitted.

But the more you enter, the better your chance of winning. :-)

CC @mayepariata