How long to steam eggs for? (Instead of hard boiling)
I like to follow Alton Brown's approach: steam for 12 minutes, drop into ice bath. Always turns out perfectly for me this way (and as a bonus, they're much easier to peel than boiled eggs).

Here's the video from Alton's show, with some extra information in it: http://www.youtube.com/watch?v=xUHKpHek2E8

And while unrelated (since you want to steam them), if you want to know everything there is to know about hard boiled eggs, this Food Lab edition on Serious Eats has you covered: http://www.seriouseats.com/2009/10/the-food-lab-science-of-how-to-cook-perfect-boiled-eggs.html