Needing help understanding ERA results for upcoming transfer!

Hi all! I did an ERA after 3 failed transfers. I did manage to get implantation but failed the 2nd beta. My results showed me to be late receptive. It was performed at 141 hours for mod natural. It was recommended that transfer be performed at 129 +\- 3 hours from HCG trigger (12 hrs earlier than when the biopsy was performed).

I triggered on 4/28. My transfer is 5/4. I asked about the timing but I was told something to the effect of starting the progesterone later (4/29 at 2002, then on 4/30 802 and 2002 onwards) to account for this. Can someone help explain this better to me?

Thank you all in advance!