He manages to meet his self-imposed deadline with just over an hour to spare, Greenwich Mean.
Sherlock is aware that most people would likely term John's continued residence at Baker Street (after a few months away early on) as unhealthy, but neither of them fits comfortably within the domain of the ordinary, thank god. More significantly, it was convenient for his current purpose, which Sherlock appreciated much more than any notions of healthy behaviour as prescribed by most people.
Of course, Sherlock isn't stupid— he's not about to sneak into the flat without any warning, whether or not John is still in possession of his Sig (Sherlock assumes he is). Waking Mrs. Hudson is not a task he's prepared to undertake either; he needs to see John first.
He does, in the end, pick the lock (John has wisely changed them) and creep silently upstairs, expertly avoiding the creaking step. There will be time later for cataloguing all the changes to the flat (of which there are fewer than he'd feared, honestly; it seems he is not the only one suffering from sentiment, if the barely moved state of his books, his chair, and other incidentals are any indication). Settling to sit on the far end of the sofa, closest to the window, Sherlock pulls his phone from the pocket of his Belstaff (finally, finally able to wrap up in the familiar wool again, with only Moran left to deal with and the endgame already begun).
The cool light of the screen is brilliant in the darkness of the flat. Sherlock stares at it for a moment, considering, then punches a few keys.
I want a cup of tea. Where did you move the bags? -SH
It takes slightly more than three minutes for the thunder of bare feet down the stairs, during which time Sherlock has reconsidered the drama of the shadowy flat, and flicked on a lamp. It's enough light to illuminate John's face the moment he rushes into the living room, pistol in hand, dressed in pyjama bottoms and one of Sherlock's long-sleeved sleep shirts.
Beneath mussed hair, John's eyes are wide and impossibly dark. His mouth drops slack, and the sound that escapes him when he catches sight of Sherlock is breathy and pained. It drives Sherlock's heart against his ribs, catching all words in his throat. Then John sways, legs gone unsteady even as his gaze stays pinned as though afraid to blink, and Sherlock is on his feet in an instant, reaching out.
"John..." It is more rasping than he ever intended, as though all this time without saying the name has rusted it, and John shudders at the sound, gasping wet and wordless.
And very shortly thereafter, as Sherlock predicted might happen, he ends up nursing a black-eye and bloodied nose.
Sherlock considers it the best birthday of his adult life.