I put in my code on the website and then read the fine print where I found this
"To receive the $100 trade in value (or actual device trade in value, whichever is greater) in exchange for the Device you trade in, you must register valid email address on or before April 4, 2013 at HTC OneTM Upgrade site, you must purchase and activate a new HTC One by May 19, 2013 and mail in your used Device with a valid Proof of Purchase of your HTC One (copy of UPC or invoice/receipt showing the IMEI) post marked by June 19, 2013"
looks like I have till May 19 to buy the ONE.