Do you believe 9 am to 5pm(office time)is enough time to work?

8 hours a day is very enough to achieve your goals, if you managed it well.

yes it is more than enough.... cause our after4-5 hours of real work our productivity start deteriorating 

Of course, it is enough you are devoting50% of your conscious time (if you excludes8 hours sleep).
But make sure employee work with proper planning and sincerity and require less supervision and external control.
Focus on productivity/ effectiveness not on how much they (physically) stay in office and pretend that they are working.

Hmmm 9 is late.. better if starts at 8 to 4 ... yes sure it is enough