What is the appropriate date range to file the TM47 90-day report digitally before the expiration date?

That is a subject for discussion 😛

I would say you can file online using the web-portal from 2 weeks before the due date down until 1 week before the due date.

That means you have a one week window to apply online.

The old rules used to be from 2 weeks before right on down to the due date, but we have reports of people who were denied reporting outside the time I quoted earlier.