Plotly timeline plot show resolution?

Hi, I am new to python and plotly. I am trying to use timeline to draw process event durations.
A simple test like the following python code allows me to draw my basic requirement:

import as px
import pandas as pd

df = pd.DataFrame([
dict(Task=β€œWk1”, Start=β€˜2.1’, End=β€˜5.5’, Category=β€˜Group1’),
dict(Task=β€œWk2”, Start=β€˜5.5’, End=β€˜10.0’, Category=β€˜Group1’),
dict(Task=β€œWk3”, Start=β€˜22.3’, End=β€˜28.9’, Category=β€˜Group1’),
dict(Task=β€œWk4”, Start=β€˜12.6’, End=β€˜14.0’, Category=β€˜Group2’),
dict(Task=β€œWk5”, Start=β€˜14.0’, End=β€˜18.3’, Category=β€˜Group2’),
dict(Task=β€œWk6”, Start=β€˜18.3’, End=β€˜20.8’, Category=β€˜Group2’)

df[β€˜Start’] = pd.to_datetime(df[β€˜Start’], unit=β€˜s’)
df[β€˜End’] = pd.to_datetime(df[β€˜End’], unit=β€˜s’)

fig = px.timeline(df, x_start=β€˜Start’, x_end=β€˜End’, y=β€˜Category’, color=β€˜Task’)

where each work start time and end time are logged in microseconds (us). However, if I change the pd.to_datetime unit to β€˜us’, only a blank graph will show, without any process bar showing.

It looks like in pd.DataFrame, the datetime type is datetime64[ns], which I assume can be accurate to β€˜ns’. How can I show a timeline bar in β€˜us’ in plotly graph?

Thanks for help!