Although ictime itself does not create and manage real invoices, it does not only provide data for doing so, but it also allows for charging work like via creating a kind of "invoice". You can add reference data from the real invoice you have created in your accouting software to the "invoice" in ictime.
All basic functionality in the reporting & accounting area will work without having to define teams and price lists for a project. You can create "invoices" for historic work log entries. However, all data won't have a financial dimension in this case. To fully benefit from accounting, you should create teams and pricelists for each project where you have work log data relevant for accounting (see Project Teams). To apply price lists to existing work logs, you would need to edit and save the respective work logs.