“After the lesson,” Snape snapped.
Under the pretext of holding up a measuring cup to see if he'd poured out enough armadillo bile, Harry sneaked a sidelong glance at the pair of them. Karkaroff looked extremely worried, and Snape looked angry.
Karkaroff hovered behind Snape's desk for the rest of the double period. He seemed intent on preventing Snape from slipping away at the end of class. Keen to hear what Karkaroff wanted to say, Harry deliberately knocked over his bottle of armadillo bile with two minutes to go to the bell, which gave him an excuse to duck down behind his cauldron and mop up while the rest of the class moved noisily toward the door.
The scene is in Snape's Potion class. I don't understand "with two minutes to go to the bell". I think "the bell" is supposed to ring for the class dismissal here. But what does "go to the bell" mean? And "with two minutes" is confusing too. What does it mean exactly in this context?
-- Harry Potter and the Goblet of Fire