When you create a user list, you can decide how long a visitor's cookie stays on your list if that person doesn't visit your site again. This setting is the user list's membership duration.
Membership duration is 30 days, by default, but we recommend choosing a duration related to the length of time you expect your ad to be relevant to the user. In general, we recommend you align the membership duration with the length of your sales cycle.
Example
If you sell movie tickets, you might select a membership duration of a few days only, but if you sell cars, you might choose a duration of a few months. While it might not take too much time for people to decide they want to buy movie tickets, it generally takes longer for someone to decide to buy a car.
If you sell Valentine's Day gifts, you might choose a membership duration of a year so that you can reach the customers on your list when Valentine's Day comes around the next year.
The visitor's cookie is deleted from the list at the end of the duration if there's no activity. If the person visits your site again, the clock is reset for another 30 days or for the duration you've set.
The maximum membership duration is 540 days. If someone continuously visits a page, the clock is reset, and the visitor's cookie stays on the list.
If you change the membership duration after a list has already accumulated some cookies, the new duration is applied to both cookies that are currently on the list and cookies that were added to the list after the change.
Example
If your cookie duration is 60 days and you shorten it to 30 days, cookies that joined the list 31 - 60 days ago will be removed.
Conversely, if your duration is 30 days and you extend it to 60 days, cookies already on the list will stay on the list for up to 60 days
The number of users that you see in your account may not immediately reflect the right count after you change the membership duration.
How to optimize membership duration
Segment visitors based on how recently they visited your site
You can take advantage of the duration settings to create user lists for visitors who came in the past seven days, 14 days, and 30 days. You might see a greater response from people who have visited your site within the past seven days, so you can use one ad for visitors who are on your 7-14 day list, and a separate ad for visitors on your 15-30 day list.
Keep in mind that decreasing the duration could limit the number of potential customers you can reach.
Bid more or less, depending on the list
You might see a greater response from users who have visited your site more recently, so you can bid higher for users on your seven-day and 14-day lists, and bid lower for users who have been on the list for 15-30 days.
Duplicate your lists
If you choose a duration that's less than 30 days, you may consider creating a duplicate list that has a duration of 30 days or longer. This allows you to serve ads to those who have considered your brand in case they take longer than average to make a purchase decision.