Maximize your tweets [infographic]
I would note that every account is different. I’m not sure what is encompassed in “engagement” since I don’t want to give my info in order to download the full report, but for my library twitter account, our worst day for retweets is Friday, not Wednesday/Thursday.
Also, personally, I hate seeing tweets with “please retweet!” in them. You shouldn’t have to beg people to share your info—it should be interesting/useful enough that they *want* to share it. But that’s just me personally. :)