Most LoL events only last 3 days that include red, blue and green classes. If you dont play LoL for the next 2 days so you can complete the dungeon event you still have 5 days for the LoL event. This gives you more time and includes yellow and purple class which is unusual. Since they are having an all dungeon event weekend if you miss the red, green, and blue missions while completing the dungeon you will get a second chance.