The 11" Air has only one Thunderbolt/mDP socket so it can only handle one mDP display. It can drive dual Thunderbolt displays in daisy-chain but not dual mDP.
It's possible to do dual displays without Thunderbolt; you could use one ACD display and then one DVI using a USB>DVI converter for example. There are also USB to DisplayPort converters but they are so expensive that I would not consider those unless you happen to already have the 24" ACDs and are just trying to find a way to make use of them. You could easily buy a USB 3 to DVI converter and a DVI monitor for much less.