Followup to #21738
Addresses comments/requests from #21738.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21764?src=pr&el=h1) Report
> Merging [#21764](https://codecov.io/gh/pandas-dev/pandas/pull/21764?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8ae4358df384dc211baa58cf1c7c0e18fb94965e?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21764/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21764?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21764   +/-   ##
=======================================
  Coverage   91.93%   91.93%           
=======================================
  Files         160      160           
  Lines       49737    49737           
=======================================
  Hits        45724    45724           
  Misses       4013     4013
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <100%> (ø)` | :arrow_up: |
| #single | `41.99% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21764?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/21764/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.45% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21764?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21764?src=pr&el=footer). Last update [8ae4358...eab2ef1](https://codecov.io/gh/pandas-dev/pandas/pull/21764?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @jbrockmendel 