Hi ARP. It is currently only possible to set the outstanding amount warning to 0, 30, 60 or 90 days. This can be set in the Options tab of System Information as below:
If you have a pay-on-the-day only policy (no accounts), where any outstanding amounts are considered overdue, you can set the setting to 0 days to warn you if any amount is outstanding.
Based on feedback from other users, it generally takes more than the 7 or 14 days you have provided as an example for a client to receive the invoice, possibly process it through their health fund and then send you a payment. This is the reason why the industry generally uses a 30 day account period.