The option Invoice module for Windows has just been released. It is identical to the iOS version in terms of functionality.
The issue with the iOS version and emailing invoices is not an issue with Time Master itself. The problem is when the email is created in Apple's Mail app, it adds it as an "in-line" attachment if it is a single page PDF. Some email clients, such as web Gmail, do not know how to handle "in-line attachments" and don't display anything.