Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9800; it) AppleWebKit/534.1+ (KHTML, like Gecko) Version/6.0.0.246 Mobile Safari/534.1+)
Timewise you would be ok but a word of warning, ATH is unstable these days. Strikes can delay flights quite impredictably.
I would sincerely think about it. Do you have travel insurance, eg Amex, which could compensate the risk of the two separate itineraries?