The medical books I have are all written for doctors, so only ever talk about a 2-week luteal phase when that's not always the case.

Basically, a woman gets her sperm-friendly EWCM, ovulates on either the last day or the day after the EWCM: once she has ovulated that's luteal phase. Luteal phase is meant to be constant and can be any length, not just 14 days, though "normal" is 10-19 days. Consistantly less than 10 days means the egg may not be able to implant and more than 3 weeks is just cruel. Again, I think a day or two out isn't abnormal for a luteal phase, but like the main cycle if you're looking at differences of more than a week there's something odd going on.

If you know how long your luteal phase is normally that may save some heartache - if it's always 12-14 days then you needn't get worried about CD33 when it's only 11DPO, IYSWIM. That way you know on 16dpo it's a better time to test. There are some medications that can extend a luteal phase if it's shorter than 10 days so if you have a short one your doctor can help with that.