Pruning Leylandii trees - when in September, or when is best, to avoid disturbing birds and bats?

I have a row of Leylandii trees that were inherited with the garden. They are well established trees.
I want to get them trimmed all the way round and the height reduced a bit.
It says online to not trim April - September to avoid disturbing bird nests.
I haven't seen birds flying in and out, but they could nest in there. I do wonder if bats nest in there, as I see them flying around at dusk.
I have to get someone to help with doing this and will need to book them in advance. I was wondering when is the best time to do the pruning for not disturbing birds and bats - is the start of September OK, or should I wait until the end of September, or when would be the best time?
Thanks very much!

 

Birds seem to love the conifer types for nesting or cover so I would certainly leave alone now. We do ours in Winter usually so leave as late as reasonable in September or after.

 

Thanks ever so much, I might leave them until early October then.

 

I'm pretty certain that bats roost in eaves, attics, cellars etc but never heard of them using Leylandii.

 

Thank you noisette47! There is a shed with eaves by the trees, or maybe they roost somewhere else altogether, in other eaves, attics, cellars. I hope they are protected wherever they are. The leylandii are mature with old wood and a hollowed inside with lots of crossing branches and crevices, so it is possible they could roost there. Apparently there are 3 broad roost types - built structures, underground sites, and trees.
I just found a site online with a leaflet with advice on tree maintenance and bats, I'll put the links below in case anyone comes across this thread for advice.
Roosts in trees - Bat roosts - Bat Conservation Trust
https://cdn.bats.org.uk/uploads/pdf/Bats-Trees.pdf?v=1541085197
It looks like early October could be a good time for my pruning.