English Language

No matter how many extra classes I've had already, I regularly get in trouble translating some Russian phrases, not even supposing how those might sound in English. So here's the question: how can I ask about the fact when students have usual classes which begin early in the morning but sometimes these classes start a little later. For example, how is a student supposed to ask his mate about tomorrow's classes if those start later? How to make this question more grammatical?