I noticed that I received interest on a deposit that completed only shortly before the daily interest was posted. That got me thinking that if someone was really paranoid you could time your deposits to clear just before the daily return rate is calculated, and then withdraw again right after. Then repeat. This would minimize the amount of time your btc is on the site. Issues are of course that the deposit/withdrawal times can vary (I've had one clear in minutes and another take ~8hrs) and the time at which the daily rate is calculated seems to change as well (I've only been watching for a few days). Not sure if this strategy would work out given the time frame and the unknown variables but I thought it might be worth mentioning. Good luck!
It doesn't always work out that way; generally when I make a deposit, I don't get credit for having it in my account when that day's results are posted. Out of five or six deposits I've only had it happen once.
Their posting times vary a lot, I imagine it has to do with how busy they were with trading that day. Generally it happens in the late afternoon PST, but occasionally it'll be around noon. Switzerland time that's either midnight, or early evening.
Ok yeah sounds like I may have just gotten lucky then...