Because I like to back sweeten with honey, I routinely do this once the ferment has finished and it's been stabilised, but before it's cleared.
Honey has a bad habit of causing a haze in already cleared batches, so I find that if I back sweeten to hydrometer numbers (I like my meads at about the 1.010 area), then any haze that might come from the sweetening honey, generally drops out with the other particulates.