My husband and I never talked about when we would try for our second child. We knew we wanted another, but it wasn't up for discussion because money was tight and having 1 baby and a 12 year old (from my 1st marriage) was very expensive.
Surprise, surprise - when my daughter was 6 mos old I found out I was pregnant. We were shocked although my husband was more excited than me. It turns out to be the best thing that ever happened. My kids are 15 months apart. The first year was pretty rough - diapers for 2, formula (again!!!), and my daughter really was still a baby.
My son will be 2 on Sunday and my daughter turned 3 in August. She is potty trained and the baby is doing more everyday as he grows. They fight alot, but they also constantly look for each other. When Meghan leaves, Aidan cries and vice versa. I am glad I had them close. I only wish that my oldest wasn't so much older than them. He is now 15 and LOVES them, but he will always be the much older sibling and won't have the connection the 2 little ones have. Although, he will be able to help guide them through his behavior. He is a great kid in advanced placement classes, honor roll, volunteers at the VA, making him a great moral guidepost to look up to.
I don't believe there is a right time. Whatever happens and how it happens doesn't matter. It all works out in the end. Go with your gut:)