Identifying content to present to a group of online system users based on user actions and specified by a third-party system

A method comprising:

• receiving, by a processor of an online system, tracking pixel data corresponding to a plurality of actions performed by a first user of the online system on a third-party site, wherein each action performed by the first user is recorded by a tracking pixel embedded on the third-party site and has a timestamp indicating when the action was performed;
• adding, by the processor, a first user profile of the first user to a first target group in response to identifying that a first action of the first user in the tracking pixel data satisfies a user property of the first target group, wherein the user property of the first target group defines eligibility for inclusion in the first target group, comprising a target action and a predetermined time interval associated with the target action, and wherein the first action of the first user satisfies the target action of the first target group and the timestamp associated with the first action is within the predetermined time interval associated with the target action;
• identifying, by the processor, an opportunity to present content items to the first user of the online system;
• identifying candidate content requests from a first set of content requests directed to the first target group, wherein the candidate content requests comprise a threshold number of targeting criteria satisfied by characteristics in the first user profile of the first user;
• selecting, by the processor, using a content selection technique performed by the online system, one of the candidate content requests with a first content item to present to the first user based at least in part on the characteristics in the first user profile;
• and
• presenting, by the processor, a first content item of the selected candidate content request on a client device of the first user.

A non-transitory computer-readable medium storing instructions, which when executed by a processor, cause the processor to:

• receive tracking pixel data corresponding to a plurality of actions performed by a first user of an online system on a third-party site, wherein each action performed by the first user is recorded by a tracking pixel embedded on the third-party site and has a timestamp indicating when the action was performed;
• add a first user profile of the first user to a first target group in response to identifying that a first action of the first user in the tracking pixel data satisfies a user property of the first target group, wherein the user property of the first target group defines eligibility for inclusion in the first target group, comprising a target action and a predetermined time interval associated with the target action, and wherein the first action of the first user satisfies the target action of the first target group and the timestamp associated with the first action is within the predetermined time interval associated with the target action;
• identify an opportunity to present content items to the first user of the online system;
• identify candidate content requests from a first set of content requests directed to the first target group, wherein the candidate content requests comprise a threshold number of targeting criteria satisfied by characteristics in the first user profile of the first user;
• select, using a content selection technique performed by the online system, one of the candidate content requests with a first content item to present to the first user based at least in part on the characteristics in the first user profile;
• and
• present a first content item of the selected candidate content request on a client device of the first user.