Screenshots in Behavior Map are taken every day - if the page has been visited by a website user.
If the page has not been visited then screenshots will still be taken each Wednesday and again on the 1st of each month.
Screenshots will only be available for the period after the page has been added to the Behavior Map feature.
Screenshots are stored indefinitely, unless the page is deleted and not added again within 30 days.
Screenshots are taken at midnight CET.