For DHCPv4 the lease time is respected, but for DHCPv6 Luci says that the lease time remaining is "unlimited". I have a OpenWrt client which does respect the lease time.
That leasetime is only for for IPv4 by default. It even mentions that in the DHCPv6 wiki:
leasetime string 12h DHCPv4 address leasetime
It seems you'd be looking for:
ra_useleasetime bool 0 Use configured leasetime as
limit for the preferred and
valid lifetime of a prefix
But, I noticed that is a boolean value...meaning, when enabled to 1, it will change from infinity; and will use the IPv4 leasetime value. Hope this helps.
Looks like I have the same problem, I even set ra_useleasetime to 1 and still no lease time set for dhcp reservation hosts. It still says unlimited for IPv6.
ra_useleasetime should be enabled in all the default installation of OpenWRT. I have a guest router and its IPv6 stops working after I reboot the main router. Once I enabled ra_useleasetime to 1 and set the static lease to 1 day for guest router now the IPv6 comes back within a day. Also there is a bug in LUCI which should correctly show the lease time as 1 day instead of unlimited. Hope this gets fixed soon. How do I report this bug?