I'm pretty sure it isn't.

I actually proposed a cooldown for apt-get in my PhD thesis in 2013 and calculated its impact. Because the meta-data for the Ubuntu apt repository can be completely downloaded you can simulate the impact of a cooldown on how many less packages would be installed and it isn't zero.

There are always people in a community running beta version, or up to date versions. There will be less with a cool down, but then depending on how critical your system is you could adjust cooldown length