In my opinion, I wouldn't start playing a freeroll tournament having only 30 mins available. In the tournaments I have been so far, 2 h is not so uncommon for a Tournament to take - sometimes they take even longer.
Apart from the discussion, whether or not it would be fair to shove each single Hand, I would not understand the Point of joining a Tournament where I cannot see the Hand. Even if you are lucky and create a big stack - if you sit out after 30 mins, chances are that your opponents have reached or surpassed you and you will blind out eventually.
As for me, I like to play tournaments not only because of chances to get free money, but also in order to learn and improve the play every day and because I like to take time for playing poker. If I don't have a lot of time to play poker, I would prefer playing a quick cashgame. If i don't want to spend
real money, I would play with play money..
Cheers