Ipv6 ra_lifetime is always 604800 seconds

KONG 20 r16991-7371c0b849 / LuCI Master git-21.163.60157-1bcb125
Kernel Version 5.4.124
Netgear R7800

I'm using the latest nss build from KONG on my r7800 and I have the following problem:
Adjusting the dhcp setting 'ra_lifetime' on the webui or the config files has no effect, the advertised valid and preferred lifetimes are always 604800 seconds.
(it can be observed with the command 'ip monitor prefix' on the client machines)

Why is this a problem for me?

Each time my internet connection restarts my ISP will hand out a brand new /64 prefix which means that the old addresses need to be purged from the client machines as soon as possible, because they are useless and if they remain active as 'preferred' addresses, they will cause the client's ipv6 connection to fail until they expire.

Now, it is true that when a reconnection occurs odhcpd will re-advertise the old prefixes as invalid (preferred lifetime of zero, this is again, observable with 'ip monitor prefix') but if the entire router is restarted and not just the internet connection, no such invalidation will occur, and my clients will be stuck with a 'preferred' but broken global ipv6 address.

Being able to advertise a really short valid + preferred lifetime via odhcp would solve this issue, but again, the setting doesn't seem to work.

Also, I can't find a separate setting for 'valid' and 'preferred' lifetimes, I think that those should be available.

Thanks for reading, any help would be appreciated.