I'm full time job in consulting/biz dev and getting my start-up off the ground. I've been using (boomerang for gamil) boomeranggmail.com and seriously, I don't have to remember about sending emails or following-up (key in both biz dev and start-ups). I'm surprised most people I've met don't know it/use it.
It's a nice product. I accomplish something similar using Google Inbox delays/reminders, and by not caring about my email timestamps. :) If I was in a situation where sent time reflected on me, I would certainly use it, though.