I am sorry but currently, there is no way to set the default time frame filter value to Custom Time Frame.
The only workaround solution would be
- create a custom date field
- create a scheduled flow which runs overnight to populate the custom date field
- set the default Time Frame as Last quarter
- design flow to update the custom field of the records earlier than last quarter (e.g. records between 1/1/2017 - 31/12/2019) to the date within the last quarter (e.g. 1/1/2020)