Hi,
it should be an error in the text as discussed here: https://elearning.di.unipi.it/mod/forum/discuss.php?d=2575
The withdrawal phase should be in between the submission and the opening phases, to give the chances to someone to forfait the competition and get back half of their deposit.
So the order is: Submissions -> Withdrawal -> Opening, and they should not overlap.
I hope to not be wrong. If I am, I will notify it.