Last year it was two Saturday games, one on Sunday and one on Monday.
The year before that, it was one on Friday, one on Saturday and two on Sunday.
I think it depends on what the TV companies want. The final Six Nations games are all on the same Saturday, so that might have an impact. BT have Liverpool v Watford in the Premier League on Saturday evening, and BBC are showing the rugby at the same time. So definitely no Saturday evening game, but probably one Saturday lunchtime game. Likely to be two on Sunday and then the other either on Friday or Monday night.