First round of letrozole- when do we BD?

So I started my first of 5 days of letrozole- today is cycle day 5 for me- I normally ovulate between cd16- 21- but I know letrozole will make me ovulate earlier- my question is when do we start to BD? My dr said to start OPKs cd10 so should we start to BD at least every other day now? I'm over thinking this whole thing but I'm nervous it's my first time trying meds and I'm super sensitive to birth control so I'm concerned this won't be anything like I'm used to for a cycle- but then I guess that is the whole point- sorry for the rambling!