Road construction is done during peak traffic hours because that is the best time for them to work as the asphalt companies are open as well during those times.
It's also cheaper to do road construction during peak traffic hours and during the daylight hours than to do it at night.
At night they would need lighting which is costly and it also becomes more dangerous to be out working on the roads and highways at night.
Asphalt also cures better when it's hotter outside and so that's another reason it's done during peak hours but also some road construction is done when it's cool or cold out.
If the road construction is just done early morning, night etc then it would take longer to get the road construction done.
We all have to deal with the road construction traffic but we should be thankful as well that the roads are getting improved.
However some road construction is carried out at night on major highways that they close off lanes for the night to get things done such as building bridges, widening roads etc.