10-15 minutes sounds like a dream! I would plan on tacking on 2 hours just to give yourself a cushion, though for me, the border has always been faster than the airport. It totally depends on who is at the border, though; I have had a busload of people waiting to be processed..and that was at 2:30 a.m. Normally, though, you are dealing with cars vs planefuls of passengers. Also, it depends on who is looking at your letter-it is so individual. Best results have been during the day when officers are knowledgeable about
TN and can decipher your letter properly. I had one guy actually say that he took a few basic courses in my field (2 or 3 degree levels below mine) and he "just knew" that I was missing a few sentences, so he told me to fix it and I had to turn around and come back. I added a few extraneous things and then I was yelled at by the same guy who NOW said that my letter was a copy (I realize now it has to be an original) but that didn't seem to matter to other officials). Thank goodness, I had Hilton points...I stayed at a Hampton for two extra nights getting the documentation straight for this guy who really was trying to poke holes in a letter that really couldn't be expanded all that much. I also missed my plane. Thank goodness for South West Airlines, not charging me for changing a reservation. Not taking a chance the next time round, I phoned the POE Monday, spoke to a senior guy who was relaxed, knowledgeable about TNS, had no point to prove, and said "come on over...get a FAX from your work and barring any glaring problems, I will let you in, no problem". He chuckled when I arrived and alluded to the fact that a lot of officials on weekends have no clue about the TN. All I could say is that guy was a sweetheart and am grateful to him, as I actually made the next plane to the US. I would make the letter solid (look at sample TNs and what they are looking for), bring all supporting docs (transcripts, diplomas, etc) and you will have a better leg to stand on. At the border, the official will type up an I-94 for you with "Multiple Entry" stamped on it, the expiry date (a yr to 3 yrs from the date your TN is issued) vs the I-94 that you write yourself. They will then write the name of your facility in your passport with the date, staple it into the passport, which they will then stamp. Hope that helps!