The following is from flybmi.com
Online Check-in is available on bmi operated flights. This service becomes available 24 hours before the scheduled departure time and will remain open right up until 30 minutes before departure for UK domestic and Western European shorthaul flights, and 45 minutes prior to departure for all other routes.
Online check-in closes 1 hour before departure if travelling from Addis Ababa, Almaty, Amman, Amritsar, Baku, Beirut, Bishkek, Cairo, Casablanca, Dammam, Freetown, Jeddah, Marrakech, Riyadh, Tbilisi, Tehran, Tripoli or Yerevan.