Nice, good catch!
testing this out this seems to introduce a (much more minor) bug with regular non-reversed axes when the tick corresponding to the first tick label is just out-of-range, we get the full 2-line label twice:

It'd be nice to include jasmine tests for ^^ both forward and reversed, with the original range shifted in something like 6-hour increments - so ranges:

['2019-12-29', '2020-01-04']
['2019-12-29 06', '2020-01-04 06']
['2019-12-29 12', '2020-01-04 12']
['2019-12-29 18', '2020-01-04 18']
['2020-01-04 18', '2019-12-29 18']
['2020-01-04 12', '2019-12-29 12']
['2020-01-04 06', '2019-12-29 06']
['2020-01-04', '2019-12-29']

And just check that the tick text we get in each case is as expected. Something like that should cover all the related cases, I'd think.

@alexcjohnson in order not to intersect with #5065, I need to merge this PR and work on the fix for #5065 (comment).
I could address your comment above afterwards.
So merging...