As regards NATS units, for a stand-alone Tower such as Luton, the initial unit training ("Transitional Training") lasts just over two weeks - classroom lectures followed by simulator training and including a written progress test at the end of the Transitional Training phase.
On-the-job training (OJT) then lasts for around 12 to 14 weeks. Obviously, for a controller who is not an ab-initio trainee i.e. has come from another unit, depending on that unit's task, OJT at Luton could last for around 8 weeks.
For units having an approach radar function on-site (e.g. Birmingham, Bristol, Glasgow, Edinburgh), the process repeats itself (some trainees instead, start on radar and then move on to ADI training).
For the area units, the process of OJT is significantly longer as sector training and endorsement is progressive.
So too is the OJT at somewhere like Heathrow and Gatwick towers - for obvious reasons.
Training Times in each unit's Approved Unit Training Plan are specified as a number of hours (minimum, target and permitted maximum).