I definitely couldn't do it without a folded towel and a pillow on top of it: I rest my backbone/spine on the edge of the pillow, with my legs resting out in front of the pillow on the ground. I should probably buy a zafu. Not having one would also make me wince; I figured everyone used pillows or something. The rest is more intuitive: legs crossed, spine/neck straight (level gaze, head back, but chin down), relaxed shoulders. More info is in the guide I linked to in the post.

Were you making notes as you went or did you remember all this, with fairly precise durations, afterwards?

I remembered it fairly precisely, and the times are all based off of post hoc guessing. It's a bad sign I guess that I can remember all that, 'cuz it means I wasn't really focused on my breath. I got a little too meta, I think: thinking about my meditation. I tried to pull my attention back to my breath and I did get some subtle facial numbness I associate with jhana (perhaps incorrectly) but I wasn't able to keep it going long enough. (Also, thinking "Ah yes, I'm getting close to a jhana!" is a very natural and somewhat derailing thought.) Still though, the overall experience was very refreshing and peaceful. I'm not surprised that most people don't have as intense an experience I had on their first try, but I am surprised that they don't experience the subtler but still strong experiences of peacefulness, compassion, patience, even physical enjoyment, et cetera. Perhaps reading Mindfulness in Plain English would help?