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/1662#issuecomment-339730597,https://api.github.com/repos/pydata/xarray/issues/1662,339730597,MDEyOklzc3VlQ29tbWVudDMzOTczMDU5Nw==,1217238,2017-10-26T16:56:03Z,2017-10-26T16:56:03Z,MEMBER,"I'm pretty sure this used to work in some form. I definitely worked with a dataset in the infancy of xarray that had coordinates with missing times.

The current issue appears to be that pandas represents the `NaT` values as an integer, and then (predictably) suffers from numeric overflow:
```
In [8]: import pandas as pd

In [9]: pd.to_timedelta(['24658 days 11:15:00', 'NaT']) + pd.Timestamp('1950-01-01')
---------------------------------------------------------------------------
OverflowError                             Traceback (most recent call last)
<ipython-input-9-cc287bf4c401> in <module>()
----> 1 pd.to_timedelta(['24658 days 11:15:00', 'NaT']) + pd.Timestamp('1950-01-01')

~/conda/envs/xarray-py36/lib/python3.6/site-packages/pandas/core/indexes/datetimelike.py in __add__(self, other)
    658                 return self.shift(other)
    659             elif isinstance(other, (Timestamp, datetime)):
--> 660                 return self._add_datelike(other)
    661             else:  # pragma: no cover
    662                 return NotImplemented

~/conda/envs/xarray-py36/lib/python3.6/site-packages/pandas/core/indexes/timedeltas.py in _add_datelike(self, other)
    354             other = Timestamp(other)
    355             i8 = self.asi8
--> 356             result = checked_add_with_arr(i8, other.value)
    357             result = self._maybe_mask_results(result, fill_value=iNaT)
    358         return DatetimeIndex(result, name=self.name, copy=False)

~/conda/envs/xarray-py36/lib/python3.6/site-packages/pandas/core/algorithms.py in checked_add_with_arr(arr, b, arr_mask, b_mask)
    889
    890     if to_raise:
--> 891         raise OverflowError(""Overflow in int64 addition"")
    892     return arr + b
    893

OverflowError: Overflow in int64 addition
```

This appears to be specific to our use of a `TimedeltaIndex`. Overflow doesn't appear if you add either value as scalars:
```
In [11]: pd.NaT + pd.Timestamp('1950-01-01')
Out[11]: NaT

In [12]: pd.Timedelta('24658 days 11:15:00') + pd.Timestamp('1950-01-01')
Out[12]: Timestamp('2017-07-06 11:15:00')
```
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