When does a deposit expire?

Questioner

I sold a device via a Marktplaats for 8,000 euros and received a deposit of 1,000 euros. However, the wait for the collection now takes 4 weeks. Or in other words: how long should I reasonably wait until the buyer collects his purchase and pays the remaining amount? It seems to me that after 6 weeks, for example, I can conclude that the purchase did not take place and the deposit expires. What is the advice / are there regulations for this?

Lawyer

If no delivery date has been agreed, the claim is immediately due. Therefore, you can still set a date for the buyer to pick up the item from you.