This Integer32 (0 or 60..2147483647 seconds) is described as the number of seconds before the SA is completely deleted, forcing a new phase-1 negotiation if the connection is still active, with 0 meaning the lifetime is not conveyed to the remote side. An admin sets this on the reusable policy entry so every crypto map referencing it inherits a consistent full-renegotiation interval. For example, an admin standardizing security posture across many tunnels would set this to 28800 seconds (8 hours) on a shared IKE policy rather than configuring lifetimes per crypto map.