My company is considering to work with an international IT company to implement an ERP system in our workflow.

This is our first time working with this kind of cooperation (usually we just buy a package of the product and implementation), so my boss is curious how the billing works. I know a bit (from the Workplace), but I don't know what happens when this scenario happens.

The engineer will have to customize a module a bit for us. When doing that, he is stuck and does not know how to proceed. Then he decides to take a walk for 30 minutes for refreshing his mind.

Is this 30 minutes walk billable to us? What if he takes a 4 hour walk? Is this any different whether he work on our premise or remotely? And if it is billable to us why are we expected to pay it?

Both of our companies are located in Indonesia. Our partner is an Indonesian branch of an international IT company.

Please note we are not asking if it is billable in a specific case, but to understand how it usually works since we have never worked with an outside consultant programmer.