I think it must vary from place to place and patient to patient: my initial treatments took 10 mins each (plus 'getting you into position' time; the boosts were only 5 mins. Not long enough to fall asleep! (I nearly nodded off during one of the early sessions...) Last one tomorrow!
I had clear margins and no lymph involvement but had 5 booster sessions on top of the 15 normal ones.
The sessions were quite quick and at our unit, almost always on time unless a machine had broken down which only happened a couple of times while I was there. The actual 'treatment' only took about 5 minutes but I was generally on the table for about 20 mins in total as it can sometimes take a while to get you into the right position (I seemed to be particularly awkward with this bit!). The best advice I can give you for this bit is to totally play dead - do not try to move yourself on the table to help them, the movements they will need are so tiny and they are experts at doing it, so just let yourself go and they will 'mould' you to where they need you.
I am relieved to hear of the underarm problems - I have the same but haven't mentioned it as I thought it was all due to the lymph node clearance (my onc says the various odd feelings could take 2-3 years to resolve!)
But I guess it makes sense that an area that is already compromised will be affected by the rads. I am certainly putting the moisturising gel well into the underarm, but that doesn't stop it feeling stiff and sore, much more than the breast area. But the threatened tiredness has yet to strike: I must admit the steps in the tube station are a little steeper than they were a couple of weeks ago, but nothing like the cliff face during chemo - I would drag myself up them clinging on to the hand rail for dear life! And any lethargy at present is I am sure entirely due to the hot weather, which I hate!
I've just finished 15 rads with 5 boosts to come this week. WLE had clear margins first time round, so presumably they're just scheduling them to be on the safe side (TNBC). The whole process is pretty painless (literally) so far so I'm not complaining!