Here’s what the lawyer says
Under Swiss law, Sven must check the goods “as soon as is practicable in accordance with the ordinary course of business” and report any defects discovered to the seller “immediately”. The duration of the obligation to check and report defects is not strictly regulated by law, but depends on the circumstances of the individual case. However, the courts are strict and generally only grant short time limits (a few days; in the case of perishable goods, possibly just a few hours, otherwise around seven days).
The situation is different for hidden defects, i.e. defects that cannot be detected even upon careful inspection. Sven must report such defects immediately after they are discovered. Otherwise, he will forfeit all rights relating to defects. Sven can document the defect with photos or a detailed written description.
He must send the report to the seller. As he has concluded the contract with the shop, he can assert his contractual rights against the shop. The shop cannot simply refer him to the manufacturer.
However, the manufacturer may also have provided a guarantee. In this case, depending on the content of the guarantee, Sven can also request a repair directly from the manufacturer, for example.