Depends upon your riding experience, eyesight and route. Interstates are definitely safer at night than rural two lanes or any highway with intersections. Interstates are fenced so less chance of critters wandering into traffic. Requires a level of attention managing other traffic and crap in the road (potholes, tar snakes and frost heaves).
Nighttime usually brings on a decreased level of attention due to lack of sleep (you and other drivers) and lack of things to look at to relieve boredom. More drunks on the road especially following bar closing time. Rain, fog, or high winds at night can be decidedly more dangerous than during daytime and I would not travel at night with the possibility of ice or snow. Most of the other traffic on Interstates at night will be trucks (buffeting, water splash etc.) and rest areas will fill up with idling trucks reducing your options to pull off and rest your eyes or catch a nap.
I've been across the country multiple times on I-80, I-70, I-10 and I-5 from Seattle to Phoenix. I've driven both cars and bikes non-stop from Phoenix to NYC, Richmond to Chicago, Phoenix to Orange, TX (and then to middle FL the next day) and from NYC to Northern CA. I have spent as much as 18 consecutive hours on a bike (middle NE to Phoenix) but am too old to do that again. The eyes are still good but they won't stay open as long as years ago and I find nighttime boring and too dangerous for me to drive long distances at night. Plus, you miss seeing the countryside in large part.
Just my two cents.