Last year the k.o times were 12.30, 3pm and 6pm. The least attractive of the three fixtures was the lunchtime one. I think you can easily argue that Sheff Utd v Blackburn is the least attractive this year, so my guess is that will be the lunchtime fixture. Given the distance Grimsby fans have to...
I'm pretty sure it can't be 5.30 on the Saturday, as Sky has Chelsea v Everton live. And obvs they won't have both Manchester teams at home on the same day. So my guess would be Man City v Burnley on Saturday lunchtime, then the three other games on the Sunday (as they did last year).
You’d like to think that the two matches where fans have furthest to travel are on the Sunday -ie, us and the Man Utd game (which, as you say, has to be Sunday anyway).