Understanding the breakdown of an invoice is key to manage allocation of costs. By getting clarity on where costs are being incurred you can make decisions on whether to continue or cease certain tasks. Hence an early decision and agreement on time tracking tools is a key starting point for the project.
This has to be offset by the extra effort to record and compile data. It is important to decide the resolution and accuracy that is required at the start of a project. If you are using a supplier to provide outsource software development then discuss and agree both the invoice and level of supporting materials as early as possible.
There a variety of time tracking tools that are available, here is a list of a few: