Last year, it was split between CBS and TBS. I believe CBS gets first choice. Last year, CBS chose the West Region so it went like this:

West Region: 7pm ET on CBS
East Region: 7:30pm ET on TBS
West Region: 9:30pm ET on CBS
East Region: 10pm ET on TBS

Time zone means nothing and seeding means nothing.

We could see the Newark games start at 10pm ET or later. However, I am guessing Duke advances and if that happens CBS would likely choose the East Region for Thursday. CBS views the 9:30pm ET slot as more desirable so I'd guess if BYU advances to Newark they'd be at 7pm ET on CBS and Duke would be the 9:30pm ET slot. (North Carolina was a 1 seed last year and UNC got the 9:30pm ET slot on CBS on Thursday . . . so that tells me the 1 seed doesn't get preferential treatment when it comes to rest for a potential Saturday E8 matchup.)