Hey Aspirant !
As far as the schedule of 1st Year MBBS is concerned, there's nothing called as 'afternoon classes' itself.
The schedule of every day includes classes beginning right at 8 am or 9 am and it continues till 4-5pm in the evening. You may miss the lectures at your own concern, but skipping practical classes isn't advised.
Now, the management between theory and practical classes depends on every college and there's no fixed time schedule to it.

Hope this helps.

Good luck !