The safest time of day to travel is before 8:00 AM when most people are not on the road.
When the roads don't have as much traffic it makes those roads much safer to travel on.
So if you need to be at work in the morning it would be best to leave out at 7:00 AM if you need to be at work at 8:00 AM.
Of course the time you leave for work will depend on when you have to be at work and sometimes you still have to drive on the roads when it's not the safest.
If I'm going on a road trip I like to leave out during the darkness before it gets daylight because I can get through the high trafficked roads such as the interstate with less traffic and then I can get onto the less traveled roads by daylight.
So I leave out around 4:00 AM to get through most of the heavy highway and interstate traffic and it's much calmer driving during the dark when not too many people are zooming past me.