Considering the fact that Bangladesh borders West bengal..which is not far from Bihar and UP..So, i guess enough Army can be mobilized in 12-15 hours at max..
Ask your army strategists, it will take over 60 days. So, take your time and come to BD land. There will be an welcome ceremony for your coward army. Last time in 1971, you escaped with only 1300 deaths, because we gave our lives in many lakhs, instead. But, this time you should be ready to give 13 million lives. So, who stops you from coming? Just jump.