I think the 40/60 split is a good one
Quite flexible - there is an expectation to come into the office 3 days a week but there is a very good culture of allowing people to set hours that work for them e.g. working around appointments, commitments with kids.
I work the typical 9-5 day and it seems this is quite normal. I think we are flexible when it comes to hours as it is possible to start/leave earlier or later.
I am very happy with the work-life balance at bp, particularly as a grad. I work hard within my working hours and there are times where I have to work late. But, my managers are very focused on my wellbeing and always make sure that I take the time back.