时间框架格式不包含“ h,m,s”

I got a timeframe with the following format: '%Y-%m-%dT%H:%M:%S.%f'

I want to group my timeframes by same days, but that's difficult with the different time (h, m, s). So I wanted to change the format to '%Y-%m-%d'...

tags_regularity['Timestamp']= pd.to_datetime(tags_regularity['Timestamp'],format='%Y-%m-%d')

但现在的格式是这样的:

2020-01-14 04:56:11.761001500

我的错误在哪里?没有错误信息。