Anyone know how/when to harvest these?
Look at the pods that develop at the base of each flower. When one turns brown and crusty, there are teeny, tiny seeds inside. They should be there now, further down the stem. Spread the seeds on a paper plate and allow to dry for a day and then save them in a tiny ziploc bag or paper envelope in a dark, cool, dry place till next spring when you can start them early indoors (about 8 weeks before the last frost.)
If you tap the little capsule where the flower was, and it breaks open, the seeds are mature. The pod breaks in half, the top comes off as a little dome full of black seeds. It's cute.
I have found for seed-saving in general that empty film containers to work nicely. Either save your own or ask at a film drop-off counter.
I prefer empty prescription bottles, as they are see through.