X-axes with numbered days and time - but without dates

I am looking for a way to setup the x-axes to show numbered days and time - but no dates.

The goal is to have two traces that compare values for June with values from July - for this reason dates on the x-axes do not make sense. But between custom day 1 to day 31 labels it would be great to still have time-of-day labels to show automatically when zooming in.

Here is an example screenshot:

Instead of “Jun 29, 2017” I would like to display “Day 29”, but still keep the hour labels.

You can do so by setting xaxis.tickformat

See https://community.plotly.com/search?q=tickformat for some examples.