[ at rosinante's comments, daylight makes an affirmative sound. ]

Dr. Solis explained the first bomb gave away their position and it took a while for the World Eater to reach them. It probably means they saw it approaching them and tried to get it before it reached them.

[ which did not work. leading to- ] When they used all four... I guess they had done it from somewhere safe, like before they retreated to the mines, wherever that is. Some bombs and missiles can be controlled through remote access or even put it on a countdown. Giving them time to escape.