Silas naturally knew just how saving his father and Kim in less than 3 minutes is beyond impossible with his current base speed of 20 mph.
With his current speed, it would take him 20 minutes to get home and save his Dad and it would take him 2 hours, 15 minutes to get to San Francisco, and save Kim.
With this just trying to save his Dad alone is already more than five over the time limit he has and the bombs would had already exploded before he even covers quarter of the distance.
While the time limit also applies to Alex, he's safe because the distance to the hospital is short and she would also be one to operate on him.
It's naturally impossible for human surgeons to successfully operate on his brother and take out the bomb.
Under normal circumstances, surgeries are very delicate procedures and very stringent, and careful preparations are always made before it's done.
