The cooldown is negative and the quest cannot be completed again.
Cooldown was set to 480 in the properties.

If I had to guess I'd say my quest caching system missed updating repeatable tasks. Hopefully can get this fixed by next update

It works now, but the cooldown doesn't start at 8 min, but around 24 sec instead...

Seems to divide by 20

480/20 is 24 sec

Ok, so it's just a visual bug. repeatTime is set to 600, and it thinks 600 is 10 min.

That's not a bug, the cooldown is in game ticks not seconds. 20 ticks = 1 second

(does math in head) yeaaaaa... that's wrong. I should probably fix that next update. Thanks for the heads up