One thing that concerns me... the value of washing coins is based on the time between the deposit and the withdraw. If you deposit and withdraw the same amounts with no delay you diminish the value of mixing. On top of that... the ChipMixer paradigm is based on creating a session that terminates after 7 days. Meaning... if I create a session and deposit some bitcoin I need to preserve the chips or withdraw the BTC within 7 days.
So what if the BTC is sitting in my session and the 7 day session expires while the site is down? In this case I never really had the chance to withdraw the funds.
First of all, the best anonymity is achieved by keeping some time between deposit and withdrawal, that's correct.
But you don't have to withdraw within 7 days; you're supposed to 'withdraw' vouchers right away, and redeem and 'actually withdraw' the coins potentially months or years later.
In the rare chance that you did create a session, deposited and had no time to withdraw keys or chips / vouchers before it suddenly went down, don't worry. ChipMixer extends session times by the amount of days that it was offline. That's at least how they did it so far.