How long does cookie consent last in Saudi Arabia?

The PDPL sets no expiry date for consent. It lasts until the visitor withdraws it, which they can do at any time, or until you want to use the data for a new purpose, which needs fresh consent. How often you ask again is your decision: state the period in your cookie policy and keep to it.

Three rules shape that decision. The purpose of processing may not be changed without consent (Article 5). Personal data is destroyed once it is no longer needed for its purpose (Article 18). And withdrawing consent must be as easy as giving it or easier, after which processing stops without undue delay (Implementing Regulation, Article 12).

So ask again whenever you add a tag with a new purpose, such as a first advertising pixel on a site that only ran analytics. Keep each earlier answer in the record rather than overwriting it, so you can still show when and by what means it was given (Implementing Regulation, Article 11).