When should I test?

My issue is a bit complicated. I’m 30 days since last period, haven’t gotten a positive opk yet, although I’ve never gotten a positive on them, even when I conceived my son. The last year or so, periods have been sporadic at best, and between 45 and 80 days apart so I’m unsure when it would be “late” for me to test. 2 days ago, I had spotting that lasted a few hours, with mild cramping, and is completely gone now. Still not having my usual signs of AF either.

I know IB is rare, and I’m not even sure that’s what my spotting was. I didn’t have IB with my first pregnancy. But if it was IB, when should I test? Anyone have insight about how long it takes for HCG levels to be high enough for FRER to detect?

Thanks!