>>>is it a speed camera?
Almost certainly not.
I supervise traffic surveys for one firm and help out with them for another. We use cameras (or 'automated traffic counters', with rubber tubes across the road), rather than people, to monitor traffic flows wherever possible. The cameras are usually attached to lamposts, with large boxes at the foot of those posts holding the batteries and/or data recorders.
You seem to have described the type of equipment that we use. Further, the time at which you discovered it corresponds with the practice of our guy who puts them up, which is to install them in the early morning (because he's fed up of answering lots of questions - or even having the police called - by people who think that he's some form of terrorist or simply intent on invading their privacy).
That white box will probably have a company name on it (such as 'Count On Us Ltd', 'CTS Traffic and Transportation Ltd', 'PCC Traffic Information Consultancy' or 'National Data Collection Ltd'), or possibly the name of your county council. If it's anything like that it's part of a data collection exercise which might include recording the speeds of vehicles but WITHOUT linking the speed to a specific registration number.