Yeah I did it. It depends on what times you are going to do it and which one you'll start with.
We started in Scotland at about 2 in the afternoon. Which was totally fine. You'd have no issues on Nevis.
Scaffle Pike was in the dark at about 2am I think. I couldn't see any of the drops (if there were any) so it was irrelevant - might actually work better for you. It was beautiful when the sun came up as we descended and I didn't see anything that would have been an issue.
Snowden I actually found a bit harder. Perhaps because we were all shattered by then and the path we took was a bit steeper (not the tourist one). There were definitely small parts of climbing in this one. But by then you are so invested, determination to complete the challenge sets in.
My best advice would be to do it with a guide. Ours kept us on the safe paths, had a van and driver for us, and had plenty hints and tips.
Knee supports are a must. I didn't take them as I've never had a knee issue - but you can't account for the strain the descents put on your body and I've had a knee issue ever since.
Lots of clean socks, break your boots in properly, plenty water and glucose snacks. Waterproofs were essential too (and that was in July!). Gloves - I was shocked at how cold it was at the top of Nevis, and Scaffle at night.
It was awesome. It's one of the things I'm really proud of doing and we raised shed loads for charity in the process too. Go for it!!