Milk - surges can easily last more than one day.
As an example I had three positives (ie a LH surge) which did not result in ovulation. Then 5 days later I had another two positives which did result in ovulation (according to temps). So it's like the body builds for it, then if it doesn't happen hormone levels level out and then they try again a few days later.
Typically my temp rise (evidencing ovulation) happens three days after my first positive test, though last month it was the next day whilst I still had a positive test.
They say the most fertile days are ov-3, ov-2, ov-1, ov and ov +1. So if you ov on a Sunday the best days to dtd are Thursday-Monday.
So depending on your pattern of ov date compared to OPK positive there is a further variance. So for me, assuming ov happens three full days after first positive, I should dtd on the day I get my first positive for 5days straight. However if Ov the day after my first positive (like I did this month) I should dtd from two days before my positive OPK through for 5days.
Plus the extra complication that a temp rise proves ovulation, but some people's temp rises a short while after ovulation not necessarily same day.
So allin all, no matter whether you temp, or OPK or use monitors or symptom spot, no one ever knows 100% exactly when the ovulate 