I'm not sure with the way of self.data.index[0] is at the moment, if they are date objects you could use it straight away.  Also, instead of using isoformat and extract from 0 to 19, I would just write the format directly as:
```python
self.data.index[0].strftime('%Y-%m-%d %H:%M:%S UT')
```
This would make more clear what we are taking from the date.