Starting next month! The article says that;
Tube Lines said the schedule for the Northern Line upgrade was still being discussed with TfL. "We have worked very closely with London Underground to find a way of getting access to the track while producing minimum disruption to the service. It is an ongoing discussion between us,"I'm fairly sure closing the line down early every working day does not count as "minimum disruption".
The private contractors responsible are still making plenty of money for their share holders but refusing to provide anything like the service a city like London needs to function. Oh well, we'll see what happens I suppose.