That only happens if your server have 5 or more active groups.
2 on Wednesday for qualifiers (I think this happen as long as there are 2 or more groups)
Then 3 rounds on Saturday for final, this requires 5-8 groups, 3-4 is 2 rounds and 1-2 is one round (or maybe no war if there is only 1, I'm not sure)
I assume it's a weekly mission? You can reroll those if it's an impossible one on your server.

no, top 4 out of 5-8 would get the full 3 round.
Thou it's true that 5-8 won't.

Also, the "top 4" isn't really by strength, because the match up of first round is random. Whoever loses in the first round are tossed out.