Comment 10 for bug 1761096

Since Sergio mentioned groovy, this really only is a xenial issue:

Test:
1. install dnsqmasq+squid
2. ensure dnsmasq is able to run (port collision >=Focal)
3. stop/start dnsmasq in a loop

for i in $(seq 1 4); do date; echo "-"; systemctl stop dnsmasq; date; echo "+"; systemctl start dnsmasq; date; done

Xenial: slow
Bionic: fast
Focal: fast
Groovy: fast

Xenial:
Wed Sep 2 06:24:15 UTC 2020
-
Wed Sep 2 06:24:15 UTC 2020
+
Job for dnsmasq.service failed because a timeout was exceeded. See "systemctl status dnsmasq.service" and "journalctl -xe" for details.
Wed Sep 2 06:25:46 UTC 2020
Wed Sep 2 06:25:46 UTC 2020
-
Wed Sep 2 06:25:46 UTC 2020
+
Wed Sep 2 06:25:47 UTC 2020
Wed Sep 2 06:25:47 UTC 2020
-
Wed Sep 2 06:25:47 UTC 2020
+
Job for dnsmasq.service failed because a timeout was exceeded. See "systemctl status dnsmasq.service" and "journalctl -xe" for details.
Wed Sep 2 06:27:18 UTC 2020
Wed Sep 2 06:27:18 UTC 2020
-
Wed Sep 2 06:27:18 UTC 2020
+
Wed Sep 2 06:27:18 UTC 2020

So as the bug was already flagged, this is really only a xenial issue anymore.
And the fact that it is "ok" for squid to take 30 second for a restart is intentional as outlined above.