The 3.14.0 release of Scap (current version) added the --canary-wait-time option to the sync subcommand (which the next version of Scap will rename to sync-world). This sets the time how long Scap waits for code to run on canary servers. The default is 20 seconds, but if that is too long or too short, you can now adjust it.

As usual, please use carefully. Don't shorten the time just to make your deployment go faster.

https://phabricator.wikimedia.org/T217924