Oestradiol patches day 15 or 16?

[Koala365]

Has anyone done a protocol where they started using oestradiol 100mcg patches part way through their cycle then started stimulation injections at their next period? My protocol says to start the patches on Day 15 or Day 16. At one point on the phone the nurse definitely said in passing start on Day 15 at another point she said Day 16. Day 15 would be tomorrow (Saturday) and Day 16 Sunday and I am not sure whether there is any science to which Day I start them. The clinic is now closed until Monday. If you have used these patches, what Day were you told to start them? Thank you!