how many hours should i charge my new iphone

Keep it charging for 1-2 hours after display says 100% charged.

Thanks for the points.

Let me add: don't be too much obsessed by charging times. I owned with my whife 4-5 iPhones and 3 MacBooks since 6-7 years. Always charged them without full discarge and sometimes not untill fully charged.

Done one or two times in the life of each device the suggested calibration http://support.apple.com/kb/HT1490.

Never had problems with batteries and the lasted at least 3-5 years (until I sold them still in good condition).