JackDaws on chimney

Hi 

looks like I gave some jackdaws trying to create a nest on top of my chimney, both chimneys are not in use anymore and have pots/caps

think they first start very recent as found a couple twigs below building

looks like there building it on the flat part of the chimney as cannot see anything on top of the pots, you can see some twigs.

when will these birds be gone as I want to arrange a roofer to inspect chimney condition and to do more to discourage nesting again and I have a couple of tiles I need to sort