Timeout option breaks rebuild decision

Scons does not properly detect whether a notebook needs to be rebuilt when using the timeout option:
`scons timout=360`
Instead all notebooks will be rebuilt regardless if changes were made or not. 
Directly providing a dict `{'timeout':'360'}` to the setup in the SConstruct file does result in the same issue.
Issue occured on Arch Linux using Miniconda with Python 3.7.