In game development it is usually the norm to spend a few extra hours after a beta update to make sure that there are no bugs that came back or weren't fixed.So no official release of 1.5.1 today?
It is also good to let the player base have a go at the build and check if they run in to any obvious issues that slipped by from the QA and Dev teams. If all goes good and the team feels confident to release it, it will later today. They indicated this at the last beta updates.