At work we have an Agile working policy. My understanding is as long as you do your contracted hours you are ok. I have seen people send emails and update spreadsheets at 7.30pm or even as late as 10.00pm and this is standard work not extra project work.
Though some managers don’t allow flexible working and will allow you to have an hour off for an appointment and to make up the time but if you want longer you have to book the afternoon off.
How does Agile working work?