The longer guards courses are generally the ones that are non-compliant with latest ORR guidance and best practices.
For example, take Non-Technical Skills - this for many years, was delivered as standalone training over a couple of days which is now considered very bad practice - and the overall course should have NTS integrated into it, without staff realising they've received specific training on it (if it's done right). There will be several areas like this where technology or a change in training methodology has improved the training, whilst also making it more efficient.
Then consider for some TOCs, such as Avanti there is no training required for Absolute Block, (save for specific staff working Chester/Holyhead), Tokens/Tablets etc. Similarly no need to cover DC electrification for certain depots, e.g. Edinburgh/Glasgow.
Then traction, virtually no engineering/maintenance knowledge is required for faults now - because of the various agreements with the manufacturers, or the fact it's a simple flick of a switch or a reset button before TOC policy says to get help from control.
Shunting and coupling - seriously, which TOC actually uses guards to shunt/couple in 2024? I'm sure there's a handful of depots across the country that need this, but I suspect even the staff that are trained, rarely, if ever, actually use this knowledge. Why would Avanti Train Managers need this knowledge these days? Need to know handsignals, but that's about it.
If you're a Train Manager at Glasgow, only working one traction, Class 390s, only signing Preston-Glasgow and Carlisle-Edinburgh, AC only electrification, modern signalling etc- trains are prepped at Polamdie/depots for you - 4 weeks is probably sufficient for core TM training, a week for Traction, week or two route learning, couple of weeks with a mentor.
A TM at Holyhead would probably be an additional 2-4 weeks given two traction types, Absolute Block signalling, DC electrification, and a more complex core route Holyhead to Chester and then all the way down to Euston, and diversions.