I think it will depend on how the wildcard games are scheduled and specifically when the 4th seed is playing. If the 4th seed plays Sunday, I would expect the game in Foxboro to be the following Sunday.
That's just a guess on my part but the rational being that it would be a further disadvantage if the 4th seed had a short week to prepare.
Of course, there is no guarantee that 2 wildcard upsets won't occur and then a short week for one team is unavoidable.
As for the conference championships, they usually rotate each conference's time from one year to the next so this year, the AFC would be the late game (6:00 EST) and NFC at 3:00 EST. Given that Seattle is currently the number one seed, I think this early time for them should they host it will still work.