1 induction week in Cardiff, followed by 8 full training weeks. Training is Monday to Friday. All of this is in Cardiff as well with the exception of three days around the half way point where you go back to your own depot and shadow a conductor instructor. Whilst in Cardiff you're put up in a hotel monday-friday.
After you've done all that you go back to your home depot for your rules exam, then you start route learning and also get trained on any traction you might not have already learned in Cardiff (usually 175 as it's hard to get time in one down there, they aren't often in canton - Shrewsbury and Holyhead guards get sent back to Cardiff for a day at a later point for training on MKIIIs) which with a route card as large as Crewe and Chester's will take several months. Then there's 2 weeks on the job being mentored by a conductor instructor, then you're all set to go.
This usually takes less than 26 weeks, even with the largest route cards at ATW, but 26 weeks is the point at which your salary goes up to the full rate.
FWIW, I started the first week of July, and worked my first train in mid November. I was the last on my course to work a train though,the Cardiff Valley guards (who only need just over 2 weeks of route learning) were working trains long before me.
Occasionally, if a depot is particularly short staffed, you may sign just a few core routes then start working them, coming back to sign the less important routes as time and staff availability permits.
or if it's true but it's what I've heard.