For example, I saw this at IRC:
[18:21:08] <StewardBot> (self) Matiia changed user rights for Matiia@diqwiki from (none) to checkuser with the following comment: Checking possible sockpuppet
the log entry for this is:
18:21, 1 May 2017 Matiia (talk | contribs) changed group membership for Matiia@diqwiki from (none) to CheckUser (temporary, until 18:26, 1 May 2017) (Checking possible sockpuppet)
StewardBot should show this expiry too.