while you can withdraw principal at any time, interest is only calculated and paid once per week. so that means if you deposit on a wednesday and withdraw it on a friday, the interest for those 48 hours won't be credited to (or withdrawable from) your account until the folllowing monday, after 21:00.
I'm not sure I understand this right. If I deposit some BTC on Wednesday and withdraw it on Friday, will get interest for the 48 hours the BTC was in the account, but I will get it the following Monday, after 21?
What's your opinion on emptying the account every week, and putting some BTC back in the account twice a week?