Average turn around for laptop repairs from TG is 7-10 days including courier.
THe 28 days is a maximum, after which the laptop would be replaced if the repair has not been completed. It is unusual to reach 28 days unless a part is proving difficult to source.
Have you tried asking if they have a unit that they could loan you? It is not 'usual' but a polite approach may work.
Which branch are you dealing with?