Laptops in the company still have attuids assigned to their computer name. Use ADUC or the PowerShell activedirectory module to search for computers belonging to anyone in your leadership chain. Once you find their computer, you'll want to perform a ping on their computer name, followed by nslookup to see which domain controller they are connected to. It will tell you if they are connected to VPN and are therefore not in the office.
Subsequently, make a PowerShell script that automates this whole process, and now you have a way to track RTO compliance of executives. You can run it every 20 minutes to track who is doing less than 8 hours in the office.
Once you find someone, lodge a complaint with HR indicating that you believe they are violating RTO policy.