ARMv7 takes the longest to compile. Unfortunately ccache isn't as effective on release builds, I think it's because of the additional macro settings that go in to a release build that nullify previous builds. Also most of the release build machines are separate to the test build machines so they don't get any benefit from ongoing compiles between releases. You can expect 1.5 hours for the ARMv7 builder to complete and you should normally wait for this to finish. It is possible to rush a release out if you want and add additional builds later but we normally provide ARMv7 from initial promotion.