When is my out of status start?

When your I-129 was denied, you were rendered out of status from the date your original admission (I-94) expired, i.e., from 1/22/2008. You accrued unlawful presence through 5/2009, for over a year, and are under the statutory 10-year bar. This is the law; now lawyer can change it; and the only competition possible in this case is in creative distortion of the truth by individuals hungry for your money. Since you already have an interview notice, you have little to lose by going to the embassy. You have a (very small) chance that the interviewer will be tired or incompetent and will overlook your inadmissibility. You also have an argument that you were waiting for adjudication of your I-129 and should not be penalized for it. The argument is a losing one because you stayed in the U.S. almost six months after your I-129 was denied. But, again, the consular officer might be inattentive or incompetent, so you might get lucky. Considering the high stakes and the negligible costs, the interview should not be neglected, but you need to be fully prepared for a denial.

From the dates in your question, it seems your B2 visa expired on 0/18/2008. You had filed an I-129 but it was later denied. That means you were out of status as of the expiration of your B2 visa in 2008. Even though you filed the H3 petition, once it's denied, the denial is effective as of the date of filing. You left the US in May of 2009, so you accrued more than one year of illegal presence. Therefore, you now have a 10-year bar to reentry into the U.S. Since your F2B priority date is current, you can apply for an immigrant visa now, but you will have file an application for waiver of the 10-year bar. To file the waiver application you must show that a "qualifying relative" (U.S. citizen or Resident Spouse or Parent) would suffer extreme and unusual hardship if you are not granted a waiver.