EastofKoksy,
I don't know about the present, but I'm sure around the late 1980s/early'90s the slot tolerance at EGCC was much less, -2/+5 seems to stick in my mind for some reason. Bear in mind this was in the days when much of the flow control was worked out by pen-and-paper and numerous telephone calls, before today's computer-wizardry. 'Clearance Expiry Times' were also quite common.
I gave up aerodrome control in 1996, but when -5/+10 was introduced, it did seem quite generous.