Only tried it once on an exract wheat that was using the "tea bag" method for hops of 3 20 min soaks in water that was boiled and left to cool. I assume thats the equivilent of hop additions at 60, 40 and 20. When Adding zest to this I just put it in from the start, it tasted fine, though not very pronounced, might get a bit more if you leave it in the fermentor (mine was taken out before fermenting)