When the billing is user based, you can define a per user per hour bill rate that can include regular and overtime. Billing amounts are computed based on the number of hours of approved time and the user's bill rate.
As an example, for the wall painting project, when you decide to opt for the hourly user based billing model, for each of your resource you can decide a billing rate and arrive at the billable amount of this task.

User Billing Rates
If the Company billing model is User based, these user bill rates are used to calculate the Estimated Billing and Actual Billing of tasks. Rates defined at a company level can be overridden at a project level.

When you change the User Bill rate:

Estimated Billing is recomputed for all projects that are Not Archived and for tasks which are not 100% complete.
New rate is applied to all time entries that are in "Saved" state after they are submitted for approval.
Those in "Pending approval", "Approved" or "Invoiced" continue to show the old rate. The manager can edit the time entry to change that rate if required.
Actual Billing remains the same.

Browser not supported