Most days this summer, I have a CCTV camera, with motion detection software, watching 5 occupied boxes, running from 4 in the morning until 10 at night (British Summer Time = GMT+1). I have now analysed some of the data to see how number of visits varies during each hour of the day and with date. I am posting this now, before all of the data is in, as it might be useful for people surveying colonies for occupied nest-sites [You can click on the charts to make them larger]:
The average visits per day per nest-box from this data set is 13 (min 8, max 22)
The busiest date seems to be around mid-summer's day with 109 visits to all 5 boxes on this day.
So, in conclusion, surveys, in working hours, for evidence of breeding are best carried out around mid day and around mid-summer's day. We need some corroboration of this speculative assertion from other colonies before it becomes classified as "best practice".