Just for reference:
February 10, 2015 - Ticket Drive Starts (Seattle - March 1, 2018)
June 20, 2015 - Las Vegas Expansion Application Submitted. (Seattle - February 13, 2018)
(Seattle is here)
September 29, 2015 - Black Knight Presentation to Executive Committee
December 11, 2015 - BoG Meeting
January 8, 2016 - "Secret" BoG Meeting (This is the weirdness I'm trying to avoid you all going through if/when it doesn't happen in December.)
April 6, 2016 - T-Mobile Arena opens.
June 7, 2016 - Executive Committee formally recommends expansion.
June 22, 2016 - Full Vote, Expansion announced.
July 13, 2016 - McPhee hired as GM
March 1, 2017 - Final Expansion Payment Made, Las Vegas is officially a team.
April 13, 2017 - Gallant hired as Coach.
June 17, 2017 - Protection Lists Submitted to league.
June 20-21, 2017 - Expansion Draft.
September 17th - First Preseason Game
October 6, 2017 - First Regular Season Game
This timeline, mind you, involved the prospect of a Quebec team, which may have been the reason for a delay from the December 2015 BoG meeting vote to June 2016. However, the vote/announcement falling a year prior to the expansion draft is worth noting.
This expansion had an arena ready at a much earlier date in the process than Seattle.
This expansion also had a little over 15 months to prepare for the inaugural season and went on to win the Western Conference.
I realize a good portion of us think these are two different timelines and aren't really similar, I'm just providing this to show how it unfolded in the last expansion.