Finish my daily tasks or leave office on time ?

These two go hand in hand. If you are organized, you know how to prioritize, then you will have time to finish your daily tasks and beyond, and leave office in time. Staying in the office until late proves either you did not have time to finish what you had during your working time (hence you are not very good with time management and managing your duties), or that you do not have a work-life balance at the moment.

i believe that the work hours is 8 hours , and think its more than enough to finish your daily task.

Off cours I will leave office on time depends tasks priority.