This can be interpreted as a message to "please check in without delay." It's like a popular restaurant that doesn't take reservations. It's first come, first served, and if you're late, your seat cannot be guaranteed. For domestic flights in India, check-in is required two hours before departure, so it's best to check in without delay and be first in line at the counter if possible. There are occasional changes to departure times, so it's best to check online to be sure.