So without a time clock, you can't be sure employees are at work or working? I haven't used a timeclock since my teens. I know this doesn't address your issue, but didn't realize time locks were still a thing. I only note time deviations at my current job, such as PTO or sick pay.
However, I agree with the others. Fire people who are stealing from the company. Time = money, no difference here. As IRJ pointed out, limiting this from only Onprem may cause unintended limitations and force the bad actors to do it in other ways anyways. I'd only do that if they forced me to after explaining it may not be a real solution.