Hi, I don't have a ttc prob, (though I have had a mc before both my pgs) so not sure if this is relevant, but we waited til dd was a year old before we started trying again.
I'm 28 weeks now, and Bethany is 2, and I think I've timed it right for us.
I have 2 friends who's first was only 18 months or so by the time they had their second and I think they probably find it a lot harder just because their first is still so dependant.
I guess I would start trying from the time I actually wanted to fall pregnant, if that makes sense, just in case the stars are in allignment and it all works (these things happen too)