Minecraft wiki entry for Development_versions, associated text: The time span between the first snapshot and 1.10-pre1 was only 15 days, which is abnormal when compared to previous releases.
The most recent update to be equal or faster than this was Beta 1.0 to Beta 1.1, with only 2 days passing.
1.10-pre1 was previously removed from the launcher for some time, but was added back in September 2018.