Time can't be bought or sold. We know this, because if it could be, someone would have figured out how to do it already.* It would be listed on Amazon. It's the one thing that almost everyone wants more of. Time is a measurement of the state of change of the universe. It's just a thing that happens, whether we want it to or not.
When we succumb to the rhetoric that your employer is “buying your time,” what we are really saying is that your employer has the right to direct you as they see fit during whatever time they are paying for you to be at your job. And that is true, to a point, but it shouldn't be the case that they have complete control over you, such that failure to be busy with employment related tasks for 100% of your allotted work hours is considered something as ridiculous as “time theft.”
Because you can't own someone's time, any employer who uses this ridiculous notion of “time theft” is, in fact, asserting an ownership of you, the employee, as a person. They are saying that, during your working hours, you are nothing more than a tool to be used. I shouldn't have to explain what a toxic idea this is.
The fact is that an employment relationship is an agreement for the employer to pay the employee for services rendered (or goods produced). Because of the way the world currently works**, more often than not this involves showing up at a set time everyday and performing a set list of duties for a set period of time, with some reasonable flexibility necessary to keep the business in working order. Some jobs require more flexibility in duties and schedules than others. If you are not paid for your services, this is wage theft. While money is a made up thing that exists solely because we believe in it, we have used this belief to create methods of counting and storing it, and this has facilitated the creation of rights in the possession of it. This makes it possible to actually steal an imaginary thing. But no one can “possess” time. Since theft requires you to take something that is in the possession of another, no one can steal time.
Your time is not a thing you have, it's just your perception of the way you and the things around you change. It's hard to think this way, because we have been conditioned to believe things about time that are not true. We are told that “time is money,” which isn't true. We can place a money value on time; but we can place a money value on anything. Time is money as much as time is flamingoes or chimichangas, which is to say that it is not money at all. We are told that we can manage our time, which is also patently untrue. Despite our best efforts, time marches around us no matter how much we attempt to manage it. What we can manage is our activity within time. There are other examples, but what I am trying to get at here is that we have been encouraged to believe that time is a thing which we possess and, therefore, a thing we can control.
This might seem like a pointless philosophical aside, but the way we think about things matters. If we continue to believe that it is possible to steal time from an employer, and that doing so is as bad as an employer stealing wages from an employee, then we will continue to buy into an unrealistic narrative about what duties exist between employer and employee. The phenomenon mislabeled “time theft” is not a moral issue, it's a performance issue. If an employer thinks an employee is slacking, the remedy is to either find a way to coax more productivity out of the employee or fire them. There is no moral dimension to this. There is no moral requirement to always give 100% of yourself to your job. There is a moral dimension to paying what you owe your employees. That means paying the wages that they are due, even if you are unsatisfied with their performance. If you are that unsatisfied…either coax more productivity out of them, or fire them.
Your employer is not buying your time. Your employer is offering payment for services rendered or goods produced, and those goods/services usually line up with a distinct period in time that you, your employer, their business, and their customers all happen to occupy at once. That's it.
Sorry for rambling, but this has been something that has been bugging me a lot lately, and I needed to just get it out there.
*Yes, I'm aware that we can buy things or pay for services that save time for us, and that this feels like buying time. A microwave reduces the time it takes to prep a meal. A laundry machine reduces the time it takes to wash our clothes. I'd encourage you not to think of this as buying time, but instead to think of it as buying the opportunity to do something else with the limited time that you have. Because you can't buy time.
**But we can change this, and the methods and means of production have changed multiple times over the course of human history, see, e.g., the Industrial Revolution.