For a war to end early than the scheduled time which is 5:00 PM PT, the condition is to have the battle between 2 teams have uneven members. This means that if Team 1 has 50 members and Team 2 has 49 members, Team 1 can finish the war the moment they reach 350 flame points.
However, for Team 2 to counter this, they need to reach 350 flame points first. That time will only come if and only if one or more members of the other team leaves / kicked out and provides 7 flame points. This means that the battle will be technically 49 vs 49 and a bonus 7 flame points has been given to both side. Once Team 2 reaches 350 flame points, the war will continue until the scheduled time comes.
For another scenario where both teams are 50 vs 50, the war will continue regardless if one side only has 2 members left. The important thing here is the amount of members on the team during the war declaration.