are you their supervisor?
if not, then sorry to say, but mind your own business.
i used to manage a lot of people and frankly, it's not easy keeping track of everyone, but if the job got done then i wasn't really that worried about the nit picky things people did.
one thing i didn't appreciate, though, was people tattling on other people.
you mind what you are doing and what your job is and let other people hang themselves out to dry. eventually, it will catch up to them, and if it doesn't then kudos to them for figuring out a way to buck the system and get away with it!
i know i may take an extra 15 on my lunch if i know my boss won't be there when i get back. my reason...b/c that gives me 15 more minutes to visit with my son at his daycare. you see, i go to visit him almost every day at my lunch hour so it doesn't feel like his daycare is totally raising him.
basically, just put on your big girl pants and let it go.