I usually rack at aprox 6 weeks. However, there are no hard and fast rules as to when this should be done. If your particular batch of mead is no longer fermenting very rapidly, and most of the sediment has fallen out, it can be racked at any time. On the other hand, waiting a little longer will certainly not hurt anything. I'm sorry i cant really give you a clearer answer but really every mead is different so theres no definate "right" answer to this common question. In my personal opinion...i would avoid racking too early as this may temporarily stall fermentation, and in my opinion waiting longer allws you to leave MORE sediment behind making the racking more efficent, and reduces the chances of contaminating infection. Like i said, i USUALLY rack at about 6 weeks, but i have waited as long as 4 months and have never had the problem of "yeast autolysis" that some people speak of.