I normally try and use the phone features when I restrict usage for my employees. But that depends on the type of phone you are using and if you’re willing to set the restrictions manually on every phone. Since I only have a few employees, it doesn’t bother me.
You can also look for different apps like parental control apps. The one I found was called Android Parental Control and it worked pretty well, but we switched over to BlackBerry phones and I am now searching for any apps that can do the same on a BlackBerry phone.