Segments are dynamic (whereas “lists” are not), so as long as you create segment(s) they will update themselves ongoing based upon the definition of the segment.

You just need to be mindful of using any definitions that would dynamically exclude or include someone based on changes in events leading up to “sending” your campaign.  Ie, exclude if they’ve received an email in the last week or “placed an order in the last 7 days”...these things could obviously remove folks from your list (which you may or may not want to do), so be mindful of any segment definitions that would take action you may not want it to take...as your list will dynamically update between now and your send of the campaign that includes the segment.