It's possible to allow your managers to validate the real hours of their teams without giving them the possibility to validate their own hours !
As an owner or director, go to your manager's profile > Role and permissions :
Choose if the option "Can validate own real hours" should be checked
Good to know :
The option is unchecked for managers by default
The option is only visible when you allow your managers to modify published schedules and validate shifts for his/her location.
What is the impact on your managers?
When the option is on, your manager can validate his real hours as he does with the employees.
When the option is off, your manager can declare his worked hours, i.e. give the indication of the worked hours, but you will keep the hand to validate his real hours.