They just made changes based on application dates that go into effect may 31. If you apply before May 31, you will get a passport visa stamp good for 33 months, you can enter any time in there, after May 31 you get a 30 day entry stamp in the passport and have to enter within 30 days of the effective visa date. Then you collect your permit card at a post office near your given address within 10 days or arrival. You can ask for them to grant it for the travel date you'd prefer, up to 3 months ahead. There's a sticky post about it BRP is in the subject line.
If the visa has a valid from date and a valid to date then he can enter anytime between those dates but it's in his best interest to enter with at least 30 months left on the visa to avoid having to extend FLR (M) an extra time.
Because his boss needs him within a project they are working on at the moment.
My friend wants to sound as nice as he could to his boss before he leaves. So he would like to show the boss that this is the maximum amount of time I can spend on the project according to the UK immigration rules (here is where he needs the official reference).