Do you create Timesheet for tracking actual hours spent. If yes, then you can have another Activity Type for Translation Service Overtime. For this Activity Type, you can separately define Billing Rate.
Firstly, suggestion would be to use Timesheet. It will reduce sophistication.
Secondly, in the Sales Invoice, will only one line item will be added? Perhaps you can add two line items. One for 1-8, and another for overtime. For second item, you can define %discount, or have discounted Price List Rate itself.
I think the term ‘overtime’ might be a bit misleading here as it implies to be paid more for the hassle of staying in longer then standard 8 hours.
But our approach here is different I suppose. It’s more like an order Volume. In other words:
The freelancer here is happy whether he’s busy for a whole day at a time rather then only 3 or 4 hours here and then. To encourage 8 hour orders (minimum 8 hours) a discount is granted for all hours spent. As soon the Order hits the number 8 (quantity 8 hours) a reduced price for each hour should apply.
I don’t really know timesheets yet but we do not see this matter from an employees perspective but from a solo entrepreneur’s (aka freelancer’s) perspective. Do you recommend timesheets? I fancy the fact to record the time spend inside of ERPNext just not sure whether the outcome is as expected