3GPP 24.501 v20.0.0 — the document's own text
8.2.7.17 Non-3GPP de-registration timer value
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
This IE may be included if the network needs to indicate to the UE registered over non-3GPP access the value of a non-3GPP de-registration timer value.