but... armor now have infinite durability...

Mod returns armor durability

And how long should last MK2 power armor if you for example, start with it by using some of "quick start" mods, i mean what after 1 hour my base will pollute like hell, so this mod looks really attractive, cause i want to start with some hi-tech gear, but at the same time i want lose it eventually to be forced to research it and craft back. So i really dissapointed what in this days armor doesn't have durability. So what i should expect if i stand 24/7 in high polluted area? 6 hours, 12 hours, more?

And on top of that: are biters affected by "toxin" damage? Can personal shields somehow interfere with this mod?

And how long should last MK2 power armor if you for example, start with it by using some of "quick start" mods, i mean what after 1 hour my base will pollute like hell, so this mod looks really attractive, cause i want to start with some hi-tech gear, but at the same time i want lose it eventually to be forced to research it and craft back. So i really dissapointed what in this days armor doesn't have durability. So what i should expect if i stand 24/7 in high polluted area? 6 hours, 12 hours, more?

The more pollution the faster the armor collapses. If you exit the pollution zone then the armor will continue to destroy a maximum of 1 minute.
I can not say the exact time of the destruction of the MK2 armor.

And on top of that: are biters affected by "toxin" damage? Can personal shields somehow interfere with this mod?

Biters do not receive damage from toxins.
Personal shields also do not protect against toxins. Unless modifying them through mod, adding toxin resistance