Jupyterhub-idle-culler - TypeError: '<' not supported between instances of 'str' and 'float'

I’m trying to setup jupyterhub-idle-culler as a standalone script using python 3.9.7, using the info at GitHub - jupyterhub/jupyterhub-idle-culler: JupyterHub service to cull idle servers and users. OS is Rocky Linux 8.6.

The script looks like:
export PATH=/opt/python3.9.7/bin:$PATH
/opt/python3.9.7/bin/python3.9 -m jupyterhub_idle_culler --timeout=1800 --url=http://localhost:8081/hub/api

When I run it, I get an error:

[E 220928 09:39:11 ioloop:761] Exception in callback functools.partial(<bound method IOLoop._discard_future_result of <tornado.platform.asyncio.AsyncIOMainLoop object at 0x7f89c31b7d00>>, <Task finished name=‘Task-1’ coro=<cull_idle() done, defined at /opt/python3.9.7/lib/python3.9/site-packages/jupyterhub_idle_culler/init.py:73> exception=TypeError(“‘<’ not supported between instances of ‘str’ and ‘float’”)>)
Traceback (most recent call last):
File “/opt/python3.9.7/lib/python3.9/site-packages/tornado/ioloop.py”, line 741, in _run_callback
ret = callback()
File “/opt/python3.9.7/lib/python3.9/site-packages/tornado/ioloop.py”, line 765, in _discard_future_result
File “/opt/python3.9.7/lib/python3.9/site-packages/jupyterhub_idle_culler/init.py”, line 164, in cull_idle
resp = await fetch(HTTPRequest(url=url + “/”, headers=auth_header))
File “/opt/python3.9.7/lib/python3.9/site-packages/jupyterhub_idle_culler/init.py”, line 117, in fetch
return await client.fetch(req)
File “/opt/python3.9.7/lib/python3.9/site-packages/tornado/simple_httpclient.py”, line 329, in run
min(self.request.connect_timeout, self.request.request_timeout)
TypeError: ‘<’ not supported between instances of ‘str’ and ‘float’

Any thoughts as to what might be causing this?

Thank you