Season 4 NA:

What	When
Season 4 [NA] Signups Open	3rd of November
Season 4 [NA] Signups Close	9th of February
Season 4 [NA] Seeding	10th of February
Season 4 [NA] Round 1 starts	16th of February
Season 4 [NA] Season 4 [NA] Round 8 starts (last round)	12th of April
Last dat to submit replays	17th of April
Season 4 [NA] Draw Show	19th of April
Season 4 [NA] Playoff Group Stage starts	20th of April
Season 4 [NA] Epic Cup Group Stage	20th of April - 16th of May
Season 4 [NA] Epic Cup Finals	17th of May
Season 4 [NA] Legendary and Mythic Group Stage	20th of April - 22nd of May
Season 4 [NA] Legendary Cup Finals	23rd of May
Season 4 [NA] Mythic Championship Finals	24th of May
Playoff Ends	24th of May

Season 11 EU:

What	When
Season 11 [EU] Signups Open	13th of October (20:00 CEST)
Season 11 [EU] Signups Close	17th of November (23:59 CEST)
Season 11 [EU] Seeding	18th of November
Season 11 [EU] Round 1 starts	2nd of December
Season 11 [EU] Round 3 starts	16th of December
Season 11 [EU] Christmas break	2 weeks of no matchmaking
Season 11 [EU] Round 4 starts	6th of January
Season 11 [EU] Round 10 starts (last round)	17th of February
Season 11 [EU] Last date to play regular season games	28th of February
Season 11 [EU] Draw Show	1st of March
Season 11 [EU] Playoff Group Stage starts	2nd of March
Season 11 [EU] Playoffs end	29th of March

Season 10 EU:

What	When
Season 10 [EU] Signups Open	9th of June (20:00 CEST)
Season 10 [EU] Signups Close	14th of July (23:59 CEST)
Season 10 [EU] Seeding	15th of July
Season 10 [EU] Round 1 starts	29th of July
Season 10 [EU] Last round (10) starts	30th of September
Season 10 [EU] Last date to play regular season games	11th of October
Season 10 [EU] Draw Show	13th of October
Season 10 [EU] Playoff Group Stage starts	14th of October
Season 10 [EU] Playoffs end	10th of November

Season 3 NA:

What	When
Season 3 [NA] Signups Open	23rd of June - Announced on the Draw Show
Season 3 [NA] Signups Close	4th of August (11:59 pm EST/8:59 pm PST)
Season 3 [NA] Seeding	5th of August
Season 3 [NA] Round 1 starts	2nd of September
Season 3 [NA] Last round (8) starts	21st of October
Season 3 [NA] Last date to play regular season games	1st of November
Season 3 [NA] Draw Show	3rd of November
Season 3 [NA] Playoff Group Stage starts	4th of November
Epic Cup Group Stage - Divisions 3 & 4	4th of November - 29th of November
Legendary Cup Group Stage - Division 2	4th of November - 5th of December
Mythic Championship Group Stage - Division 1	4th of November - 6th of December
Epic Cup Finals - Divisions 3 & 4	1st of December at 1pm PST
Legendary Cup Finals - Division 2	7th of December at 1pm PST
Mythic Championship Finals - Division 1	8th of December at 1pm PST
Season 3 [NA] Playoffs end	8th of December