Em a página de manual do ifconfig :
If -L flag is supplied, address lifetime is displayed for IPv6 addresses, as time offset string.
A saída é assim:
en9: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
options=4<VLAN_MTU>
ether 00:0e:ca:00:3d:0e
inet6 fe80::20e:caff:fe00:3d0e%en9 prefixlen 64 scopeid 0xe
inet 192.168.178.21 netmask 0xffffff00 broadcast 192.168.178.255
inet6 2001:db8:d:ff01:20e:caff:fe00:3d0e prefixlen 64 autoconf pltime 3385 vltime 6985
inet6 2001:db8:d:ff01:2559:b136:a7f2:67c0 prefixlen 64 autoconf temporary pltime 3385 vltime 6985
nd6 options=1<PERFORMNUD>
media: autoselect (100baseTX <full-duplex,flow-control>)
status: active
Observe o pltime
e vltime
no final das linhas inet6
.