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TimerTweaks

A War of the Chosen compatible version of the mod can be found here:
http://steamcommunity.com/sharedfiles/filedetails/?id=1125479503

Increases the turn limit by 4 for most non-story missions and 2 for UFO missions.
This should be enough to allow for a wider array of tactics, while still keeping the pace up.
This mod does not disable achievements.

Many of the kinks should have been ironed out by now, but if you stumble upon any bugs, please report them in the comments below.

A campaign reset should not be neccessary, but it is recommended. If you decide not to restart, it's a good idea to back up your save before you enable this mod.
You can find your saves at C:\Users\ Profile name \Documents\my games\XCOM2\XComGame\SaveData

If you would prefer to have the timers disabled entirely, try out http://steamcommunity.com/sharedfiles/filedetails/?id=616964599 instead.

If you'd prefer to set the mission timers to something else yourself, check out Configurable Mission Timers by wasteland_ghost: http://steamcommunity.com/sharedfiles/filedetails/?id=618055274&searchtext=

If you'd prefer the timer not to start till concealment is broken, check out True Concealment by Takeru Shirogane: http://steamcommunity.com/sharedfiles/filedetails/?id=618077830&searchtext=