Is there anyone to change is such that my all my activity starts at 0800hr and finishes at 1900hr (10hour work day)?
I have changed my settings in 'Admin Preference' ->'Time Period' ->'Hours per Time Period' to 10 hours/day and selected the "Use assigned calender to specify the number of work hours for each time period". But its still the same.
Simply change your "Original Duration" from 8 hours to 10 hours. If it is a lot of activities, perform a global change that says: If(Original Duration = 8h) Then(Original Duration = 10h), or if you prefer Then(Original Duration = Original Duration + 8h)