Sol makes more sense to me as a day than a year. Two "suns" or "sols" is a basic concept that someone from another language would find easy to translate even if I didn't know the correct word for day. A year however would be 2 "winters" or some such thing. (and no I don't mean that it would be easier for Martians to understand - They already know how to speak English from monitoring all that television.)
Although if they want to be consistant it should 7 ares make 1 aeroweek. That way they could use the same system on other planets: 7 sats make 1 satweek, 7 plutes make 1 plutoweek (and 7 uros make 3 Canadian dollars.)