I tweeted again about the online workshop on March 24th and to this day this was the most successful tweet for the course:
295 clicks (the most important metric)
I got lucky that I mentioned the conference I was going to host a hands-on version of the course. And they retweeted it (because they were friends of mine :) ) and then it took off.
I count 45 waiting list subscribers in the days surrounding that tweet. Which is pretty great. To this point my biggest growth in subscribers.
In just 7 days I went from 0 to 60 subscribers to the waiting list!