Where I work (public sector) we generally try to keep everyone working their contracted hours. There's no expectation that people will work overtime.
Occasionally something will come up that requires someone to stay a bit late and the contract is that this time may be claimed in lieu.
I think it's a good working environment. Staff generally work hard but aren't particularly under pressure. There's plenty of give and take, if they need a morning off for a school assembly etc they'll get it, it's accepted that they'll do a bit of internet browsing in work time, which is fine as long as the work gets done.
There's one member of staff who's responsible for unlocking and locking up. This is one reason staff are encouraged not to work late, if they do he has to stay late.
Anyway, usually staff are gone in good time. If there's a reason someone needs to stay more than a few minutes late the "locker up" is paid overtime. He has started claiming lieu time for every 5 - 10 minutes over his finish time. Staff have usually left at or before finish time, but he needs to lock up after them.
Staff are reminded often they need to be gone in good time, but sometimes things happen .
I'm frustrated with what seems like clock watching for every few minutes, especially as I know full well this staff member drives through the gates at his start time, rather than starts work at his start time. For most people this is something that really doesn't matter if the work gets done, but it grates that he "owes" us minutes at the start of every day when he claims every minute at the end of the day.
I also suspect heavier than average internet use (which I can check)
He does get his work done, it's this insistence on claiming this time that is the issue. Not just for locking up. As he has an early start/late finish he gets a long break in the middle of the day and he'll manage his day so he "has" to miss part of it quite often and claim that time too. Only a few minutes so no real inconvenience to him, but it soon builds up into additional days off.
So, I'm inclined to tell him I'm onto him and if he continues to claim these minutes, I'll have to start looking at the the time he's not actually working during the day.
OTOH I genuinely don't want people working unpaid and I am usually very careful to treat everyone equally. I'm not not monitoring the others, almost no one else claims anything (maybe they should).