I do not trust Poloniex. In fact I do not trust any exhange... I belive that all of the exhanges runs with negative ballance.... this is how they work (this is an example):

100 user deposit 1 BTC worth of coins: bank now have 100 BTC.
However in average will 20 user will redraw their coin at the same day, that leaves a net ballance of 80 BTC, these coins can be used by the owners to buy cars, sluts and booze.
As long as people keep depositing coins then will this work, and also the as long as the exhange grow then will there be more and more free coins, since more user are storing their coins there = more booze and sluts. When user is having delay, then is most likely because the coins are not there to be redrawn...... what can you do about it? Nothing but wait.... it is not safe to use exhanges.... the balance you see on your account is more like an "I owe you"... not a ballance.