The short answer is…when it has reached the desired taste level. Every batch of fruit is different and will require a different contact time. I know this sounds dismissive, but there is no exact answer. Fortunately, mead is quite forgiving and will hold up to numerous samplings and additions. I have a lime mead that I added lime juice to 5 different times. I kept tasting it and adjusting as I went. BTW…this mead is going to second round of NHC so I’ll stand by this method.