My last upgrade offer was received 12 days before travel via email. I was flying LHR to BKK in Y and was offered an upgrade to J for the DXB to BKK sector for GBP269. I took it in an instant. I already had lounge access being gold and the chauffeur drive at BKK is of little value as a limo into city centre can be booked for about GBP25. My hope is that EK will offer such upgrades J to F in future. Haven't seen or heard of such a beast so far.