custom date does not work?

The format date will depends on the country you set up in your QuickBooks Self-Employed (QBSE) account, Sonny8.

In QBSE, the date format aligns with the country settings of your account. For example, if you set up your account Australia, it uses the Australian date format (DD/MM/YYYY). If the account is set up for the United States, it uses the American date format (MM/DD/YYYY).

On the top of that, could you please clarify the specific custom dates you are referring to? Any additional will help us guide you efficiently.

However, if you mean the custom dates on the Reports, please follow the region date format. Please see screenshot for reference: 

If you meant something else, please don't hesitate to add a reply below.