I have a Robin that has built a nest in my front evergreens right next to my front door.
My bushes are in need of trimming but I don't want to disturb the nest.

How long would a nest be active?

Robins usually lay eggs twice, sometimes 3.

Keep an eye on the nest and make note of the activity at the nest and check if there are eggs in it. Here in SoDak the eggs are starting to hatch and the birds will be busy for the next couple weeks feeding the youngin's. Usually by the end of two weeks the babies have left the nest and the nest may, or may not, be used again. At any rate, watching the nest activity will give you some idea on how/or when to proceed.

I do no trimming until September.

Right now, we are literally covered in baby birds.

There is a nest at the corner of my shed that has the third set of birds in it. Birds everywhere.

Coincidence, I have a mother duck nesting 7 eggs, for the last 7 days, in a bush right next to my front door also. I put a bowl of water and some vegetables and berries in the area.

I had a Robins nest and the 3 eggs hatched after about 2 weeks. Then mom and dad were busy for a couple of weeks feeding them. two of the three babies died.