Magento Open Source 2.2.x
Quote Lifetime

You can determine how long a price is valid by setting the cart quote lifetime in the configuration. For example, if a shopper leaves a cart unattended after several days, the quotes price for some items might no longer be the same. By default, the quote lifetime is set to thirty days.

To configure the quote lifetime:

1. On the Admin sidebar, tap Stores. Then under Settings, choose Configuration.
2. In the panel on the left under Sales, choose Checkout.
3. Expand the Shopping Cart section.
4. In the Quote Lifetime (days) field, enter the number of days that a quoted price remains valid.
5. When complete, tap  Save Config .