AFAIR, there were two aspects to testing. The code change itself obviously only took tens of minutes, if that. First round of testing was just the build test, and that was fully automated but I think there were independent builds for multiple different hardware variations and so the total time for that was several days. Then there was actual use-case testing ... I wasn't involved in that at all, but was told it would also take several days of actual testing by a QA team.