How can I debug an action that runs with a timer?
The principles are the same that when you try to debug an user action. You just need to set the breakpoint on the action that your timer it's associated with and then wait for the debugger to reach that breakpoint, but there are a couple of things that you will need to be aware of.
The best option to debug your timer it's to manually trigger it from the Service Center, so you don't have to wait for it to run automatically.
Still, sometimes, the debug will not stop because you can have multiple front-ends on your environment and you may be connected to a different one where the timer is running. To overcome this situation you can go to Service Center > Monitoring > Timers and look for your timer log and on the Server column, see the most common server where your timer usually runs. After you have the Server, you can connect your Service Studio directly to that front-end (if it isn't yet) and then setup your breakpoint on your eSpace and trigger the timer on Service Center.