If they've swopped sperm, they can start dropping cocoons at any stage but it can take a while for the eggs to hatch. (6-8 weeks at least if you have Eisenea Foetida or red wigglers).
It's hard to know if you can influence breeding rates, especially with so few worms to start with, but from my own experience, hot composted compost is a pretty good source of food for them, and when they're happy they breed batter. The compost acts as bedding too, so it's easier to control moisture and keep all your conditions constant.
Another way of increasing your worm stock is to take a good look around your compost heaps. 'wild' worms move in after the heat dies down.

IIRC, it takes about 20 days for eggs to hatch.

Wow! sbryce, I'm impressed! At what temperature are you getting the eggs to hatch in 20 days? And in what medium? I had about 1000 cocoons in a mix of garden compost and coir and they were kept in the kitchen at about 20C, but it was a good four or five weeks before any cocoon began to hatch (and they probably weren't the freshest of cocoons). And some are still hatching 10 weeks later. But I've given up now and I'm adding them back into the general population now that it's warmed up outside.

The 20 days is not based on my own observations. I googled. I found this, which gives 3 weeks as the time it takes for eggs to hatch:

http://plantanswers.tamu.edu/publications/worm/worm.html

I just now found an article written by Kelly Slocum that gives times closer to what you gave. I trust Kelly Slocum.

http://mypeoplepc.com/members/arbra/bbb/id14.html

Perhaps you are right.

But I find this confusing. The depth of a flow through system is based on the idea that 30 days is long enough for eggs to hatch and the baby worms to migrate high enough in the vermicompost so that they do not get harvested with the vermicompost.

So now we have conflicting numbers.

I have cloths covering much of the surface of my bins, and the worms seem to like laying their eggs in the weave of the cloths- I presumed all worms liked laying eggs near the surface- maybe it's just my guys!

In a flow through bin, you add new food and bedding to the top surface of the bin every day, and remove finished vermicompost from the bottom every day. Eggs laid near the top surface of the bin will eventually work their way down toward the bottom. A flow through bin needs to be deep enough to allow the eggs to hatch and the worms to move up in the bedding before the layer they are in is removed from the bottom of the bin. Typically, a flow though bin is built deep enough to allow for 20 to 30 days for new food added to the top surface work down to the bottom of the bin.

FWIW, I never find cocoons on the top surface of my bin. find them wherever the worms are most active. What depth that is depends on how much fresh bedding there is on the top surface of the bin. The cloth that you cover your bin with provides a dark, moist, oxygen-rich environment underneath it, so you have a lot of worm activity there. AT least, that is my guess.