i see some printed ads from carriers saying they have tuition reimbursement. If you are driving 5-6 days a week OTR, that means you dont have time to take any class, then why those company say they offer tuition reimbursement ?

Tuition reimbursment means that they will pay you back the money you already spent to attend truck driving school. It does not mean they will pay for any type of new vocational or college classes once you are working for them.