While technically that's true, in most cases that's a flaw with employment contracts because such a stipulation creates wrong incentives: If an employee engages in pointless pretend work such as continuously checking emails all day long technically the time requirement of that contract has been met but the employer gets only very little value from that, if at all.

Sadly, to some extent this is - or used to be, since remote work might change that kind of culture, too - the reality in many corporate jobs, where the hours put in matter more than the results.