[jpdel]

Nope.

* PR1 is merged with main branch commit N: build OK. PR1 is merged creating main branch commit N+1 * PR2 is merged the same way creating commit N+2 * PR3 build started at the same time as PR2 build, so using main branch commit N+1 * By the time PR3 build is finished and green, head of main branch is commit N+2. So it's not safe to merge * A new build is automatically started for the merge of PR3 and main branch commit N+2. If it's green, it is merged, created main branch commit N+3.

See what I mean? (and obviously I can't figure out how to make bullets in this editor sorry ...)

With a build lasting 30 minutes, cases like PR3 above are more likely to happen. But then it doesn't really matter: the build tool will just run builds until it merges. The real issue here is the delayed feedback for the developers: if you are interrupted every 30 minutes with some build status (green or red), it's quite a waste of time daily in terms of context switching.

What CI tool and Git provider are you using? Lately I've worked with a team with a build of 28 minutes using TFS VSTS. We got the build down under 10 minutes using conditional builds (tests ran only if some folders have changed).