How is Time-out variable supposed to work?

### Describe your use-case which is not covered by existing documentation.

In the plugin configuration, there's the section "Time-out variable". My understanding was that I can use a Jenkins env variable, for example TIMEOUT=60, and assign this variable unter "Time-out variable". Consequently, I would when using strategy=Absolute not enter a value in "Timeout minutes". However, if I do this and leave the field empty, the job fails. How is "Time-out variable" supposed to work?

### Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

_No response_

### Are you interested in contributing to the documentation?

_No response_