Creating a new hires group

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We want to assign specific tasks, such as surveys, and to new hires at specific dates (30, 60, 90 days after hire). As part of our basic integration we have a field named Hire Date with all users hire date, but that field does appear to be usable in any way, not even for sorting. Any suggestions on how to group users and assign things based on the hire date field, or is there another method for creating a new hires goup?