As per section 64Vb of the Insurance Act, the insurer can provide the risk coverage only after they have received the premium for the risk coverage. Accordingly, the Insurer maintains an advance premium deposit for group policies. As long as the Insured maintains adequate premium with the Insurer, the employee is covered from day 1 of joining/ or the day as has been underwritten in the policy. In the absence of adequate premium however, coverage starts from the date of receipt of premium at the Insurers end. Hence, it is advisable to maintain sufficient advance premium deposit balance with the Insurer.
An enrollment tool to that effect should be capable of showing you the advance premium balance available at any point in time.