Everyone has their own time they think is "the" time to post.
I've found I get more responses if I post on the weekend. Friday night to Sunday morning.
Other say early morning so when people get to work......other say about 6pm-7pm as people are getting home and relaxing.
And takes a bit more work but if I have more than one listing I put links to my other ones in each Ad.....
The best time to post really depends on your own local craigslist.. How busy the category you're posting to is and when. This is why there are differing opinions on Craigslist post times. My advice is to post consistently. Craigslist allows you to repost every 48 hours.. (I believe). If your item doesn't sell, repost often!
I've found that in the Raleigh area, if I post in the late afternoon, the others posting slows a bit which keeps my post on the first page longer. Also, make sure that your title and body text has lots of search terms in it. For example, if you have a stroller you want to sell, put the brand name and "stroller" in the title at minimum (Graco Baby Stroller) In the body, include words like carriage, buggy, etc. Include as many keywords as you can, because you never know what someone else might use to search for their product. I usually leave a keyword trail at the bottom of my post.