Well I'm taking a guess on this one since no one really knows but probably 5:00am EST time because that's the time escalation came out?
JD2020 posted on his twitter that they will never know what exact time the map pack will come out so not even JD knows. This is just an estimation according to the last map pack.
Carbonfibah here, I jacked this thread and posted some of the times for everyone, this is what has happened in the past.
Eastern Standard Time - 5am
Central Standard Time - 4am
Mountain Standard Time - 3am
Pacific Standard Time - 2am
GMT (United Kingdom) - 10am