We see that approved employee holidays show as 8 hours in timesheets. (thats the daily working hours for us). 

Why does odoo put a value in the timesheets? it should be 0 as otherwise the worked hours on the timesheet for the employee is wrong. Where can this behaviour be changed?

Note that we use attendance to manage the actual working hours done, but we need timesheet  to evaluate how many of those hours present were productive.