I installed the mod, but the game does not seem to start with peace enabled!

The mod does not enable peace, only disable it after a given timeout. You have to enable Peaceful mode in map generation settings yourself.

But why doesn't the mod enable peace!?

Because blindly overriding map generation settings is potentially confusing.

Why is there a limit of 10 hours?

I'm open to discussion (please use Github issues for that), but please consider there's a point where the concept of temporary peace no longer applies to a given amount of time.