Welcome to the Community, lsefcik.

Allow me to share some information about the bill date and posting date in QuickBooks Online.

Choosing a month/date to post the transaction to the ledger isn't currently offered in QuickBooks Online. The date used when creating the transaction is the date will be reflected on the report.

I can definitely see how this feature would be useful. As a team with a massive roadmap, we have to pick new features based on the value they’ll add to the most users possible.
I'll be sure to submit feedback on your behalf. This will notify the Product Development Team that the option for choosing a month/date when entering a bill would be beneficial to running your business.

If I can be of help while working in QuickBooks, feel free to let me know by adding a reply below.