It's a safety precaution. For your protection.
Right now, blocks @ 55 min. So a day won't kill you.
Yup, but imagine that you need to send a separate transaction for every single different address you have, as you should, because otherwise your privacy is compromised, since all of your coins would be joined within the same address, a big mistake for your anonymity again.
So that means, if you received BTC 100 times under 100 different addresses, you need to make 100 different transactions into Bittrex. At current rate, that's 100 days!!!
Why is few people talking about this problem?