Does it take longer for the tax office to process the tax return if you have it prefilled?
The short answer is: No.
The prefill has no influence on the time it takes the tax office to process your tax return.
Whether you have your tax return prefilled with the help of fetched tax office data or process it completely by hand is irrelevant for the tax offices.
It is also irrelevant whether you have requested to prefill your tax return or activated it after you have already submitted your tax return. The prefill activation does not affect the processing of returns that have already been submitted.
As soon as you have submitted your tax return, your tax office will deal with it. As a rule, it then takes 6 to 12 weeks until you receive your tax statement.
You can see whether your return has been successfully submitted to the tax office in the overview of tax years by a green tick next to the corresponding tax return.