It's sort of hard to say. As far as knowing when to dtd, knowing past cycle length is great, but it doesn't necessarily tell you when you've ovulated, or how long your luteal phase is.
If I were you, I'd probably look into using ovulation tests. When you get a positive on one of those, then you know that you'll most likely be ovulating in the next 24-36 hours.
Also, temping and charting cervical fluid, will help give you a better idea when you ovulated. Not exactly helpful for this cycle, but could be helpful for next cycle, if you need it.
Anyone, please chime in if I'm wrong about any of that!