nighttime border wall construction? i sense an increase in urgency (although i welcome the results of that increase).
Probably a little too hot to work in the daytime?
There has been a fair amount of work in the dark, just to accommodate two shifts per day.
When competing on the contracts, timely delivery (speed) was an important criteria, so many successful bidders structured their proposals around two shits per day, rather than a strictly lowest cost approach. There was a declared National Emergency, after all.
So there just wasn’t enough daylight 16 hours per day, and work lighting was required. Probably some individuals are banking a lot of overtime (at premium rates) as well.
It is basically too late to try to speed up work much after the election. High rates of construction - two shifts, night work and overtime pay differentials - were baked into the cake before the contracts were awarded.