Timeline Battle is an arena where you battle others to be high ranking and get honor points for biometrics and norn stones.
Timeline Battle has a percentage ranking system. You fight other players with 3 characters and 4 assisting characters to earn points. The more points you get, the higher the rank you'll be. If you are a certain rank you will be rewarded a certain amount of crystals. If you win, you get points and if you lose, you lose points.
You can earn honor points by battling other players. When you win, you get 50 honor points. When you lose, you get 25 honor points. Honor points are used to get biometrics and norn stones.
You have 10 tries and 5 revenges. You can have up to 3 characters to fight with and 4 characters to assist. There is an icon of your assist character near the attacking buttons. When you click on it, that character goes in and uses a skill then is out. However, there is a 10 second cooldown between assists.