This is why airlines, I know for certain Air Canada, will not post a delayed departure to the USA as later than 9 PM, regardless of how late it really is, to avoid this problem. They don't want people leaving the pre-clearance area and not be able to get back in.

I experienced this first hand earlier this year. My AC Jazz flight was delayed and delayed and delayed... left after midnight. However, AC would only show the departure as 9 PM (about an hour late). I asked the gate agent why the wrong info and she very specifically said it's to avoid people "not getting back in through pre-clearance".