The way you word that makes it sound like "the maintainers" and "T-libs-api" do not consider this "okay". Reading just above the linked comment, however, puts a very different impression of the situation:
> We discussed this regression in today's @rust-lang/libs-api team meeting, and agree there's nothing to change on Rust's end. Those repos that have an old version of time in a lockfile will need to update that.
TBH that does not inspire confidence. I would expect that something claiming or aspiring to exhibit good engineering design would, as a matter of principle, avoid any breaking change of any magnitude in updates that are not intended to include breaking changes.
Not sure why people are trying to cover this up.
The change was useful, fixing an inconsistency in a commonly used type. The downside was that it broke code in 1 package out of 100,000, and only broke a bit of useless code that was accidentally left in and didn't do anything. One package just needed to delete 6 characters.
Once the new version of Rust was released, they couldn't revert it without risk of breaking new code that may have started relying on the new behavior, so it was reasonable to stick with the one known problem than potentially introduce a bunch of new ones.