The data is structured in visits. Each visit (ex: S2) is divided into several series of images in different filters. The number after each visit gives the number of the series (ex: S2.001 in filter F125LP). Some visits are spread over 1 or 2 days while some days have zero visits.
The name of each file contains the first 3 letters of the observed planet, the day of the year and year of observation, the time of observation and the instrument (ACS).