html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/5012#issuecomment-793204639,https://api.github.com/repos/pydata/xarray/issues/5012,793204639,MDEyOklzc3VlQ29tbWVudDc5MzIwNDYzOQ==,3460034,2021-03-09T00:38:37Z,2021-03-09T00:39:02Z,CONTRIBUTOR,"I'll leave the exact issue up to someone more acquainted with string and slice handling on `TimedeltaIndex`, but in case it is useful, here are two things I noticed (to hopefully speed along the troubleshooting):

1) Using pandas `Timedelta`s instead of strings (i.e., `ds.sel(time=slice(pd.Timedelta(""01:00:00""), pd.Timedelta(""01:15:00"")))`) works, giving

```
<xarray.Dataset>
Dimensions:  (time: 39, yh: 1, zh: 1)
Coordinates:
    xh       float32 ...
  * yh       (yh) float32 0.0
  * zh       (zh) float32 0.0
  * time     (time) timedelta64[ns] 01:00:00 01:07:30 ... 01:14:30 01:15:00
Data variables: (12/26)
    x        (time) float32 ...
    y        (time) float32 ...
    z        (time) float32 ...
    u        (time) float32 ...
    v        (time) float32 ...
    w        (time) float32 ...
    ...       ...
    b        (time) float32 ...
    vpg      (time) float32 ...
    zvort    (time) float32 ...
    rho      (time) float32 ...
    qsl      (time) float32 ...
    qsi      (time) float32 ...
Attributes:
    CM1 version:    cm1r20.1
    Conventions:    CF-1.7
    missing_value:  -999999.9
```

However, notice that jump in the time coordinate...which leads to

2) In the failing example, the time coordinate is non-monotonic. If we `.sortby('time')`, then `ds.sel(time=slice(""01:00:00"",""01:15:00""))` works as expected:

```
<xarray.Dataset>
Dimensions:  (time: 47, yh: 1, zh: 1)
Coordinates:
    xh       float32 1.0
  * yh       (yh) float32 0.0
  * zh       (zh) float32 0.0
  * time     (time) timedelta64[ns] 01:00:00 01:00:30 ... 01:15:00 01:15:30
Data variables: (12/26)
    x        (time) float32 ...
    y        (time) float32 ...
    z        (time) float32 ...
    u        (time) float32 ...
    v        (time) float32 ...
    w        (time) float32 ...
    ...       ...
    b        (time) float32 ...
    vpg      (time) float32 ...
    zvort    (time) float32 ...
    rho      (time) float32 ...
    qsl      (time) float32 ...
    qsi      (time) float32 ...
Attributes:
    CM1 version:    cm1r20.1
    Conventions:    CF-1.7
    missing_value:  -999999.9
```

(the working example also has a monotonic time coordinate)

And so, I would guess this is an example of string-based timedelta selection failing on non-monotonic coordinates.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,825079209