I had a disagreement with another breeder on this so wonder if there's a consensus on how many days post ovulation do you start monitoring temp to catch the drop before they whelp?

This is just what I do... a week before due date, I start taking temp (so, if due date is 63 days from ovulation, counting day of ovulation as day #1, I start taking temp twice a day on day #56). Three days before whelping due date I start taking 3 times a day. I keep a chart and I try to take the readings around the same time throughout the day.

The reason to start taking at least a week before the due date is so you get a pattern on the temps for what is typical/normal for that particular girl.

Remember though, some never drop below 99, so don't go by just the temp... or maybe it's that they did, and missed it.

I find too that after the drop to the lowest temp, I usually see a slight rise back up.

I don't start tracking temps till about day 58 - 59 depending on the bitch and her behavior and if I'm planning on leaving the house or not. I think the whole week before she's due is just irritating to the poor girl and prefer not to take temps unless I'm planning on not being home to be on call and to fully observe her behavior.
I've found temp taking not too overly accurate and like to really be there for my girls to watch and comfort them when they tell me it's getting close.
In the end you need to do what you are comfortable with.
Good luck