I had some bitcoin in this feature for months now and I have withdrawn some of the bitcoin without any problems. It is not like a fixed deposit where you need to give advance notice to withdraw your funds, it is available when you need it. 

Test it with a small amount and see if it is working for you, before you deposit more coins. I was also sceptical at first, but I get the interest as promised and it is much better than the interest that I can earn in a Bank.