Specify units in docstrings for all lifetime fields/parameters.

[judilsteve]

A better solution would be to add properties like lifetime_ts that return the lifetime as a timespan, and maybe accept lifetime values as timestamps, with a quick lifetime = lifetime.total_seconds if isinstance(lifetime, timespan) else lifetime at the top of any function that accepts a lifetime parameter.

But for now this should at least avoid confusing people.

[jborean93]

Thanks @judilsteve for the PR, when you get a chance are you able to sign off this commit with

git commit --amend --no-edit --signoff
git push --force-with-lease origin in_seconds

[jborean93]

These fixes were incorporated with #285.