Named sets with timeout

[Matt <matt-nft@mailtower.de>]

Dear nft Forum,
I’m a big friend of named sets, specially the timeout function is very 
great.
But one thing is confusing me, assume the following named:

table ip filter_v4 {
   set my_drop {
     type ipv4_addr
     flags timeout
   }
  ...
  ...
}


Then i add the following sample element to it:
   /usr/sbin/nft add set ip filter_v4 my_drop \{type ipv4_addr \; flags 
timeout \; elements=\{a.b.c.d timeout 600s  \} \;\}

All good so far, a.b.c.d is counting down as expected, begiing with 
10min.
But when i wait - say 1 minute and repeat the 'nft add set ... 600s' 
command from above then the timer remains unchanged (?)
It looks as the timer cannot get changed anymore once it has been 
initialized

Is this behavior by purpose?
And if, am I right to delete the element and re-assign it if I want to 
get the timer updated?

Many thanks
Matt