I actually harvested two butternut squash today. One looks perfectly tan and ripe and basically fell off of the wilting vine. The other one still has faint green stripes and I kind of yanked it off of the vine by accident. So, I have an experiment on my hands. I've never grown butternuts before, so I'm not sure when the best time to harvest them is. I know that this summer's consistent heat and humidity has fast-forwarded everything into ripening sooner than expected, so I wouldn't be surprised if the mostly ripe-looking squash is ready. The other one could have used a couple more weeks I think. But we'll just have to see. Though I'm anxious to cut them open, I'm going to let them ripen a couple weeks on the counter.
Here's a link to Purdue U's extension with some advice for harvesting winter squash: