There are two options for when charm recipes get built:
A build will be scheduled automatically once a change to the top-level source branch for the charm recipe is detected.
If there has been a build of the charm recipe within the previous hour, the build will not be scheduled until an hour since the last build.
If you really want the build to happen before the one-hour period is up, you can use the "Request builds" action.
Builds of the charm recipe have to be manually requested using the "Request builds" action.