That depends on your industry and product. For example, if you have a webshop, you can use the delivery period as a guide: how long does it take for the package to reach the carrier and how long before the carrier then delivers the package? Add one or two days to account for potential delays.
Another parameter, for example, is the product: is it ready to use straight out of the box or will it take a bit longer before the customer can use the product?
Here are two examples:
- Mattress: (6 weeks’ delivery time) + (1 week for issues in warehouse) + (2 weeks for the customer to get used to the product) = 63 days from purchase to delivery and use
- Running shoes: (ordered today, arrive the next day) + (2 days for unforeseen circumstances) + (2 days before the customer can put the shoes on) = 5 days from purchase to delivery and use.
If you are not satisfied with your response rate, you can try different invite periods (A/B tests).