I would apply at least 4 months before the old one expires. My wife's and mine took 100 days to approve. We had to go for interim EAD's since our RD was 90 days before my wife's EAD expired. Had the interim EAD's for two weeks before both got approved.
Since they are taking between 90 and 120 days (according to the receipt notice), I have seen 60 days on this forum, but I would not take the chance.