I would say to my knowledge that first it depends on what type of breastfeeding you are doing. If you are doing ecological breastfeeding, i.e., strict breastfeeding every 3 or so hours than this can delay ovulation for as long as 2 years, I don’t remember if it can happen later.
Unfortunately in my opinion the CCL doesn’t do a good job of really explaining post partum return to fertility, just because I think it is a very difficult time to pin-point and each women is different. So you will mostly find the answers already given which are the standard answers, so baically keep temping, and keep tracking your mucas. If you have not had a period yet you can consider yourself in post-partum still and as long as your CM is dry you can use “liberal rules” like the last dry day rule. The problem is some women get their periods first, and some women ovulate first. So you might see cervical mucas before you see a period. So you really need to keep charting.
Now if you are seriously trying to avoid than unfortunately post partum is the time of what I call extreme abstinence. You can use the last dry rule which means intercourse on the night of any dry day and never two days in a row. This, to the admission of CCL, is a very liberal rule and is how I conceived my son. So I really don’t trust this rule myself. Not to mention it is really dependent on how well you observe mucas patterns. You definately need to do cervix checks because externally you may be dry but at the cervical os there could be mucas that you don’t detect.
Now I will give you my story since my wife and I have been three cycles now post partum and experience this extremely long and trying return to fertility. My wife got her period first, and we have no evidence that she ovulated before hand. We were seriously trying to avoid so for about 4 months before this period we were abstaining. She doesn’t practice ecological breastfeeding because she works full time, so she has to feed on and off and then pump the rest for the day care to give to our son. So her fertility returned in about 5 months. The only problem is after that first period we have had 2 full cycles. One of which was anovulatory, which means we had no temperature shift and because of that we had to basically treat the whole cycle as Phase I and Phase II, so that was about 35 days of abstinence. Then in the second cycle she experience what looked like another anovulatory cycle, but we are just seeing a shift today so maybe this is a real cycle.
I will pray for you, I understand that post partum return to fertility is very hard, especially when you are seriously trying to avoid. My disappointment is the fact that CCL really only pays attention to those who are practicing ecological breastfeeding, but overall there is a general lack of information in The Art of NFP when it comes to post partum return to fertility. If you are trying to avoid, this is the time of long abstinence.
I hope some of this information helps. God Bless.