Thanks for posting in the Community space, obscuredjinn. I'm here to lend a hand.
If you track the paychecks you process in T-Sheets, then there's no need to import the actual check amount from the outside company on your QuickBooks account. By doing this, you'll avoid duplicate data since you'll import the T-Sheets employee expenses.
Additionally, if you want to connect your TSheets and QuickBooks Online account in the future, here's a helpful article that you can visit on how to: Integrate TSheets and QuickBooks Online.
As always, feel free to reach out to us again if you need more help from us. We'd be happy to guide you again.