Hello,
Unfortunately, after having considered it, we have decided to reject this suggestion because:
Some players use Nikola as "free Reroll" by releasing their Pokemon intentionally if it got bad IVs, nature, etc. and let it respawn with the help of Nikola.
This is not intended and a decrease of the cooldown would support this above mentioned "abuse".
To solve this problem and decrease the CD, we would have to make the boss spawn the legendary with the same nature, ability and iv of the released one, but as of now there are no plans for what regard doing it. If any change will be done, you'll be informed through an announcement on our official pro discord.
Since the thread seems to go off topic, I will close it now.
kind regards