I suppose, out of the summer season and holidayperiods, the weekends are good. On Saturday and Sunday you see beside the regulars, a lot of charters. But there is one BIG BUT : Paris airport authorities are re-fencing the airport and this means less spottingpoints for the enthusiasts. On some points where taking pictures was no hassle in the past, they are putting double fences (3 metres high !). According last sources the only available points after the fences will be done, are at the parallel runways oppoite the hotel (only in the morning) and the small area behind the LSG-building.
This leaves no much options.