Hello,
Thanks for reaching out. The size columns show how many people from your user list could be reached on each network. Each network (search, display, etc) has its own minimum requirements to serve your remarketing list ads. In order Please see the 'Remarketing list size' subsection of this
support article for more information on this.
The timestamp in your second screenshot is for the date and time of the last import of customer information. This would correspond to an AddUserData request.
Regards,
Matt
Google Ads API Team

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