Let me welcome you to the Intuit Community, tirsbeck.
There’s isn’t a way of adding the invoice date on the Sales Income Summary Report. This information can only be seen on the account’s quick report.
You’ll have to tailor each income account to see the invoice date. I’ll guide you on how to access this report.
For future reference, here’s a link with detailed instruction on how to fine-tune reports.
This should point you in the right direction about showing the invoice date. Let me know about your success following the steps I provided. I’ll be right here if you need further assistance.