Add annotation between line gap in plotly

I have a graph like this:

Instead of the days being on top of the symbol, I was wondering if there is a way I can add this annotation between the lines? From one dot to another. I apologize if in case, this is a possible duplicate.

This is my expected output:

This is my current code for the annotation:

    fig.add_annotation(
        go.layout.Annotation(
            x=row["order_date"],
            y=row["sales"],
            text=f"{row['time_diff']} days",
            showarrow=False,
            align='center',
            yanchor='auto',
            yshift=10,
            textangle=-0
        )

Any suggestions on how can I do this?

What you can do is create a new dataframe for your annotations by ordering your original df by the order_date, then take the average datetime and average sales between consecutive rows to determine where to place the annotations. To obtain the text, you can take the difference in time between consecutive orders.

Your dataframe for annotations would look something like this:

  time_diff  sales          order_date
0    5 days    5.0 2019-08-27 12:00:00
1   11 days    5.0 2019-09-04 12:00:00
2    0 days    7.5 2019-09-10 00:00:00
3    0 days   15.0 2019-09-10 00:00:00
4    5 days   20.0 2019-09-12 12:00:00
5    0 days   17.5 2019-09-15 00:00:00
6  139 days   15.0 2019-11-23 12:00:00
7       NaT    NaN                 NaT

And here is a figure I made using some sample data similar to yours:

import pandas as pd
import plotly.express as px
import plotly.graph_objects as go

## create sample data and figure similar to yours
df = pd.DataFrame({
    'order_date': ['2019-08-25 00:00:00','2019-08-30','2019-09-10','2019-09-10','2019-09-10','2019-09-15','2019-09-15','2020-02-01'],
    'sales': [5,5,5,10,20,20,15,15],
})
df['order_date'] = pd.to_datetime(df['order_date'])

fig = px.line(df, x='order_date', y='sales', markers=True, )
fig.update_traces(marker_color='blue', line_color='darkgrey')

## between consecutive points:
## get the difference in time, and the average sales
df_diff = pd.DataFrame({
    'time_diff': df['order_date'].diff(),
    'sales': (df['sales'] + df['sales'].shift(-1)) / 2,
})

df_diff['order_date'] = df['order_date'] + (df_diff['time_diff'] / 2).shift(-1)
df_diff['time_diff'] = df_diff['time_diff'].shift(-1)

y_axis_range = 1.25*(df.sales.max() - df.sales.min())

fig.add_trace(
    go.Scatter(
        x=df_diff["order_date"],
        y=df_diff["sales"] + 0.01*y_axis_range,
        text=df_diff["time_diff"].astype(str),
        mode='text',
        showlegend=False,
    )
)

fig.show()