Your TimeSchedules would be a relationship between Clients and Employees with two additional informations (the day and the hours). So basically it's an m:n relationship which is a belongsToMany in Laravel with pivot data.
Think about it this way:
Every Employee can work for multiple clients. But every Client can also be "handled" by multiple Employees.
That's the definition of belongsToMany.
So you could define that relationship (example in your Employee model) like this:
public function clients() {
return $this->belongsToMany(Client::class, 'TimeSchedules')
->withPivot(['yearmonthday', 'hours']);
}