Guild Wars 2

Spending points on Nature Magic trait line you will increase boon duration, but it doesn’t work with pet’s buffs. Is it working as intended?
I tried this with Guardian’s Virtues line and it’s increasing boon duration from virtues.

If you mean buffs the pet casts, pet’s don’t get their stats based on the Ranger’s stats. They have their own stats, some of which can be improved through Beastmastery points, and traits such as Expertise Training (+350 to pets’ condi damage).

I have not heard of a way to increase the duration of buffs cast by pets, though Fortifying Bond can increase duration/number of stacks on pets when both the Ranger and the pet receive the initial cast of the boon. For example, if you have Fortifying Bond and both the Ranger and the pet get 5 stacks of Might at the same time, the pet will actually end up with 10 stacks. 5 from the initial cast, and 5 from the Ranger via Fortifying Bond. I’m pretty sure boons that only stack duration, such as Swiftness and Regen, will add the duration of the original cast to the amount provided by FB. So, if an ally casts a 10-second Regen that hits both the Ranger and the pet, the Ranger will get 10 seconds of Regen, and the pet will get 15. If only the Ranger is in range of the cast, he will get 10 and the pet will get 5, since FB only gives 5 seconds of Regen to the pet.