Arborist to maintain 40 new trees?

My workplace is thinking about planting 40 new (15 gallon-ish) trees and someone on our facilities team strongly recommended we hire an arborist for the first 3 years to "maintain" the trees. What would that entail? (Both work and hour wise)? Thoughts?

I'm thinking someone would be swinging by 3 times a year for a few hours?