There is a 30-day waiting period when you buy a new policy, starting from the day you enroll in the health insurance. Also, there is a pre-existing disease and critical illness waiting period from 2-4 years depending on the insurer to insurer.
During this period, the insurance company won't pay any hospitalization charges. But this is not applicable in case of an emergency hospitalization arising out of an accident. The waiting period is not applicable for renewal of the policy for subsequent years.