Dear Sir,
To the best of my knowledge..this depends on the class of travel.
Usually major meals(i.e Lunch/Dinner) are served strating from SLC, then 2 AC followed by 3AC.
Snacks/Tea is served in the order of 2AC-3AC & SLC, while a different schedule is followed in 1AC altogether - I'm sure you will understand these diffrence based on orientation of these various...
more... classes.
However to ascertain the exact correct timings please ask the Coach Attendant/Pantry car staff for accurate information.They willguide you best ....
Hope this is order, but feel free to clarify any further query.
Wishing you a happy journey