BUG: Datetime duplicates

#### Problem description

Today I get a error from AutoML in Azuer is `Error: The specified time column, 'SolarDate', contains rows with duplicate timestamps. If your data contains multiple time series, review the time series identifier column setting to define the time series identifiers for your data. If the dataset needs to be aggregated, please provide freq and target_aggregation_function parameters and run AutoML again.` 
So I check for duplicates in 'SolarDate' - a datetime column, the result is this column is duplicated at a certain time of day 


#### Output of ``pd.show_versions()``
`df[['Solar_Date']]`
![image](https://user-images.githubusercontent.com/50236861/113598064-c9b75d00-9666-11eb-88f7-aef19500d1f8.png)
```
df['Solar_Date'] = pd.to_datetime(df['Solar_Date'],format="%Y/%m/%d %H:%M:%S")
df[df.duplicated(subset=['Solar_Date'])][['Solar_Date']]
```
![image](https://user-images.githubusercontent.com/50236861/113598183-ee133980-9666-11eb-9dee-75869aeb60db.png)


