Ever just add 20 minutes to whatever they tell you? I started doing that as my own personal buffer and it cut my waiting around by a lot. It turned their floating time into my fixed plan. After a while they just got used to me being the one who showed up exactly when expected.
Yeah I started doing that with my friend who's always late. Told her we meet at 7:30 when I really mean 8. Now we both show up at the same time, it's perfect.