I've only seen a couple, I saw a great -8 at just after dusk a few months ago. I could see it before the flash travelling slowly across the sky like other satellites I've seen, then brightened up until it was brilliant and then dimmed over just a few seconds, maybe 5 - 10 seconds or so, then I could see it for another several seconds.
I 'think' the best ones are just after dusk/sun down, I can picture it in my head but it may be hard to describe: What you are seeing is the reflection of the sun off the satellite, so just after dusk satellites have the most time before they traverse into the earth's shadow.
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