I had some problems with the downloading as well. It seems that the website is not always functioning very well, so Walter sent me the files another way.
Yes be careful and do not overdo it. I started the first week with 20 minutes long tones in the morning, plus som practising in the late afternoon, and ended up with another 20 minutes long tones before going to bed. It was too much for me – I lost 2-3 tones on top of my range. I guess my lips got swollen. Now I’m doing the 20 minutes only once a day and I feel much better. I think the routine with long tones can build embouchure if we take it slowly.