Using FRER tests, they showed positive at 8dp3dt, or 11dpo. At 10dpo tests were still very negative. My betas were done 14 dpo and were just over 100, very normal range. If they had been lower, it may have taken longer than 11dpo for me. It does depend on your body makeup, BMI, and how diluted your urine is.
I agree that the very early positives are mostly twins, extremely unlikely for your case.