i'm not the best with OPKs...I think once you get the + you could O anytime in the next 12-24 hours (maybe even 48 hours?). I got in habit of taking OPK both in AM & PM on the day before, on & day after I anticipated Oing so I could try to narrow the window down a little. I counted 1DPO as the next day after I got neg OPK after having positive OPK (keeping in mind that I could get a + in the AM, and the neg in PM on same day, and then the very next day could be 1DPO).
I think if you DTD's Monday, today, tomorrow and Friday you've pretty much covered all of your bases though

so I don't think you should worry....good luck to you I hope this is your lucky cycle!!