Okay, I don't know if this part was in the prelim patch notes or if this was stated already in this thread, but...

Players who select Withdraw from the Duty Ready confirmation window or allow the window to time out without making a selection three times or more in one day, will be temporarily prohibited from registering for duties via the Duty Finder.
Do you know what "or more" means? That it will be possible to withdraw more than three times, but hey they also said "temporarily prohibited", connect the dots and what do you get? After the third withdraw you will have a short lockout, after the short lockout you still can withdraw and still get locked out.

To dumb it down a bit more, you have 3 withdraws with no penalty, after that every withdraw will have a penalty until the counter resets and then you will have three free withdraws again, this penalty will probably be just a few minutes, less than the penalty for joining and leaving (otherwise people would exploit that penalty).

I personally expect something like 5 minutes, any higher than 5 and people will start entering instances and asking to be vote kicked.