Help ScFi book can't name or author

[thefeds]

Can anyone help out. I read this book years ago and lent it out and like the old story it didn't come back

It is about a fellow in central America area, who falls and wakes up in the past time of the Aztec or Myan but I gravitate more to the Aztec. At the time of Cortés and The Spanish Conquest this man gains the respect of the people and knowing the history he help them change history in their favour. the book is sort of like fact meets fiction. I am not 100% sure but may have "time" in its title but again don't trust that fact. Also thought towards Frank Herberts but it doesn't seem to be.

I have been searching for a very long time. I would like a copy so I could share with my kids.

Thank You in advance.