Actually you can fast track construction safely by having around the clock shifts. I was in construction for 35 years, many time sensitive projects ran around the clock. Multiple shifts means a fresh rested crew each shift. The issue becomes the cost, after hour shifts are typically paid a " shift differential " not exactly OT but none the less more money. Another note, many Disney projects do have some night work. Much of it is to bring in prefabricated items that they don't want the public to see. Such as "Slinky Dog" I saw him come in on flat bed trailers covered up with tarps. This happened with a few trucks after 1:00 am. There are many other cases I have witnessed, too numerous to mention. But pouring the cement for Gaurdians is another example, it went all through the night. It's on the internet in time lapse video. Also putting the bridge beams in place and pouring the cement road bed over them. So to answer the question through the night construction does happen at WDW.You can't fast track construction safely... I'd rather 3 months longer than a coaster derailed...