We used ecological breastfeeding, which is a version of LAM (requires co-sleeping, no pacis, nap with baby, no solids until 6 months, nurse on demand throughout the day and night). My cycles returned at 9.5 months postpartum, with ovulation, which is on the early side, statistically. It took another 4 cycles before my luteal phase was long enough to sustain a pregnancy, I believe. Pre-baby, my cycles were always 24-26 days long, but those first postpartum cycles lasted 43, 33, then 23 days, with ovulation 5-8 days before the end of the cycle. Around 13 months postpartum, my cycles were pretty regular again, and I felt a noticeable hormonal change--I felt like my old self again. We made a point of avoiding pregnancy for a couple cycles, then stopped avoiding, and now I'm due with #2 in March--exactly 2 years after my son.
So I'd say that LAM alone avoided pregnancy for 13 or 14 months. It was great to go so long before cycling. I had mucus from 2 months postpartum onward, which was disconcerting, but I got used to it, and I could tell when it switched to a more fertile mucus pre-ovulation.
I had 2 years of NFP experience pre-baby.
Mama to Peter (3/8/04), Leo (3/12/06), Timothy (7/24/10), and boy #4 due on the summer solstice 2014