Question about nests and tree works - quick response appreciated.

Hope everyone is well and safe at this rather unusual time!

We have some gardening works happening in our area today and this includes trimming an evergreen in the neighbouring garden. I saw a couple of collared doves hang out near this tree and fly in and out a few times over the weekend. I was wondering how to tell if they have begun making a nest? It's too dense to really see into it. How often would the birds need to fly in and out? It's possible that they were just visiting after all but if they are indeed making a nest, I would like to inform the tree workers. If I don't see the birds for over an hour, is it safe to assume that they are settling elsewhere?

Thanks!