Can one ovulate on day 23 of a 30 day cycle?

Yes. However, the second half of the cycle (luteal phase) is generally consistent lasting for 12 to 14 days. Thus, you more likely ovulated around days 14 to days 16. The follicular phase is the part that can vary significantly. While lh testing can be helpful, sonograms are the most accurate to assess for follicle recruitment and ovulation.