^^^
Star Trek made $17 million on the Sat-Sun of its third weekend, and that was with the inflated business of Memorial Day weekend. $18-20 million for Sat-Sun for STiD on a regular weekend would be a Herculean task. I think it'll make $18-21 million for the full Friday-to-Sunday weekend.
I don't think a trend upwards is impossible, so far After Earth is 17% fresh. The scifi fans will go see STID.
RAMA