Hi Von . by law it's illegal to interfere with a nest as soon as the 1st piece of nest material has been laid...I understand its not in an ideal location expecially unter a bird table! If this has already happened then best to leave and Do Not put any food anywhere near the table or box as this will only attract predators and other birds....if the birds are only just inspecting the now a would perhaps put it away in a shed or something until the window cleaner can put in a better location.....ideally this cleaning should really be done in September/October and repositioned for winter roosting and next breeding season .
As I am not an expert this is only my personal opinion and will happily be corrected if I have given any wrong information ;-)
(Pardon the Scottish Accent)