Ex-Openreach here, worked there 2010-2012 but left to go travelling.
Everything in my post is based on working for them then, however I believe new recruits now have a very different contract and it isn't as easy.
There is a few different sides to Openreach, ideally you want to be installing and fixing faults on residential/business lines, rather than pulling in cable, working away from home in the cold
Everything is stat based, and in the eyes of the engineers it doesn't work, but as long as you know how to "play the game" it can be a great job, which can earn you decent money (Nothing spectacular unless you move up through the management chain) and when I was there the hours were great.
In the winter I worked Monday-Friday (With the odd Saturday, with a day off during the week) 8am-3:40pm, and in the summer, 4 days a week, 8am-5:40pm.
You'll have to pass a "logical reasoning" test before the interview stage, and the interview is pretty standard and should end with a colour blind test.
If you get the job normally you'll go away all expenses paid for a week or two to a training centre to learn the basics, but best advice would be to befriend older and more experience engineers as there is so many tricks and little things to make your life a lot easier
Any questions send me a trust message