Mostly to save the space... I'm also using the YYYYMMDDhhmmss value as an integer so converting it back is slightly easier to visualize... I had already written and implemented the logic before I'd considered Math.floor(now/1000).toString(32) which would only be 7 chars.
I'm using grate for database migrations and just wanting to capture versioning that matches the project(s)... the release version is tagged to the release number, but every merge/push into master gets deployed to a shared dev db.... I wanted to better track those deployments... I'm also now adding a link to the repo url for the commit that was deployed.
In the end, it's mostly for uniqueness, and the githash is probably more valuable than the timestamp, I just wanted it there.
They're both going to be 9 characters (base 32 or base 36), also It's a bit pedantic but base32 is more broadly supported, and part of the same standard as base64.
https://www.rfc-editor.org/rfc/rfc4648#section-6