This thread contains the completion times for various people, in response to someone asking the same question you did. The hours for completion ranged from 40-65. The total completion varies - some are for 100%, some for much less.
Another thread asking the same question had an average completion of around 50 hours, although some people took as little as 25 hours (for second playthrough), and one person took 120 hours for their first play through and 242 for their second (I think there numbers might be off though... for obvious reasons). A few other threads have people clocking in around 40-50 hours as well, with a few people going as low as 20 hours for the first playthrough. The last thread also has a poll, with the majority taking 40+ hours.
A few other Q&A sites have times ranging from 40-60 hours as well. This Sorean person took about 20 hours, although not sure if I trust that Stack Exchange site... some pretty shifty folk on there.
IGN's review states:
It'll keep you busy for at least 50
hours and you could spend double that
in Nintendo's new Hyrule. So much to
do and see that you'll be busy for
weeks, if not months.
In response to a question posed by Kotaku, Nintendo reps stated the game has 70 hours of gameplay.
Howlongtobeat.com has the average for the main quest at 34 hours, and an average of 57 hours to achieve 100%. The average for all players was 48 hours.
As you can see, on average it takes people anywhere from 40-60 hours for their first play through; although some people completed it in half that time, and others over double. In other words, it depends on a combination of your skill level and how much exploration you do.