The correct answer would be 5 years, 1 month and 12 days.
Because knowing my luck I would get the text from the beautiful woman while I was driving. I would try to answer the text, end up in a terrible accident, wake up in some hospital after being in coma for 5 years, send the phone in for repair, get it back 30 days later and spend 12 days answering text messages until I finally got to the text from the beautiful woman.
So my answer...5 years, 1 month and 12 days. :-)
All kidding aside, I would say texts should be answered within 2 hours. I do know that my phone sometimes goes into weird mode where I don't receive text responses until 1 or 2 days AFTER the text was sent.