How can I parse free-text time intervals in Python, ranging from years to seconds?

how about pytimeparse lib

Returns the time as a number of seconds:

from pytimeparse.timeparse import timeparse
>>> timeparse('33m')
1980
>>> timeparse('2h33m')
9180
>>> timeparse('4:17')
257
>>> timeparse('5hr34m56s')
20096
>>> timeparse('1.2 minutes')
72

source seems to be here https://github.com/wroberts/pytimeparse