Q: Time Machine makes some hourly backups but not all of them (macOS 1.12 Sierra)

I would like to see Time Machine making hourly backups instead of the relatively random schedule it follows on my system.

• Mac Pro (Mid 2012)
• macOS 1.12 Sierra
• Bought last week from a company that specializes in used Macs. Apart from this problem the system runs perfectly.
• Time Machine is setup to put backups on an internal hard drive. I used the disk utility to erase the hard drive and formatted it with one partition, using GUID Partition Map. I repeated this process a few time, and deleted com.apple.TimeMachine.plist /Library/Preferences on the system drive, which is named air_force on this system. I named the drive air_force, to distinguish it from the other drives, which are not as fast as the system drive.