Perhaps it will help that the mass of weight bearing down on it all, including the beam in question, is gradually lightening by the minute. Horvath can't go as fast as he'd like, for fear of causing some sudden avalanche that will doom those beneath. If Horvath is stronger magically, more experienced, more skilled than Danny, he is still every bit as terrified that at any second something will shift wrong and there will be a scream and it will be entirely his fault...

Because he is older and more experienced, Horvath is capable of compartmentalizing that fear and focusing on the work at hand. With Hermione's guidance he's able to excavate in a careful cone-shaped area, occasionally making use of some of the debris he's moving to brace other parts to make sure the edges don't collapse inwards. It may take what feels like an eternity for those trapped below, but eventually, they'll see light coming through the rubble from above, and feel the air.

Actually, that probably makes it colder. The rubble was at least some insulation from the frigid air.