SallyJ - with Confirm, in my experience, a faint line shows that O is on it's way. When I used Confirm, I got about 4 days of gradually getting darker 2nd line before a positive was registered. So I reckon you could start BDing from tomorrow night, if today was your first faint line. So O may actually still be 3 or 4 days away (don't quote me on it as it might be different for you).

With Fortel OPKs, i've noticed a difference - i seem to get a sudden positive (with no faint line lead-up), or only one day of a faint line.