He hasn't started yet, loads of inertia yet to over come to get things moving.
I reckon there is about two years of 'siting' of targets, maybe the odd improvement here and there, to come first, then third year he starts to make some incremental gains and fourth year the main aims and 'ways and means' become clear.... enough to get Labour re-elected in 2029.
Then part two of the actual 'moving the dial' kicks in around 2030-32.
It all depends on how much 'head wind' he encounters, both from other parties, notably Reform (if his plans for ending the boat saga doesn't work) and what are the likely other 'unplanned or unavoidable 'events', plus the 'revolts' occurring in Labour that will slow him down or drive him off course.
It also all depends on the man himself and the people immediately around him, Starmer doesn't need to be an all 'singing and dancing populist', a Blair Mk2, etc. he just needs to be a man who sets his face like flint and gets the job done.
In my opinion there is no quick fix, and if the dial doesn't move, in the next ten years, it never will.