Having looked at a couple of houses in Castledawson, it seems like the some of the 4 bed houses are out because of the size of the bedrooms (the two main bedrooms are too small) and the distance from the development to the station is hard to judge due to the fact that the bridge is down, but it seems to me that it would be at least 10 minutes, if not more.
It doesn't seem to make good sense to buy in Castledawson for convenience if there is little or no difference versus Moyglare Village/Abbey, especially since Castledawson houses seem to sell at a small premium to Moyglare. Having said that, Castledawson seems like a nice quiet development, and the only thing that I would have an issue with is that the main road in the development remains unfinished, and will probably remain so for another year at least, judging by progress on the development at the back.
Re. the bridge under construction, is September a realistic timeframe for completion? There certainly seems like there is a lot of work to be done.