There's a lot of reasons, sometimes you're waiting for a DOT inspector to bless off on something before you can move on, sometimes it just rained and you can't get proper compaction until the moisture level comes back down, or it could be as simple as man hours have already been used up for key operators for the week and they might not want overtime. lately I suspect unexpected delays are from supply shortages for culvert pipe or whatever. I use arch linux btw.