First, that isn't what you actually said. Also no it doesn't. It takes a fraction of a second on a single core for each block. It's 900KB for a full block.

First, that isn't what you actually said. Also no it doesn't. It takes a fraction of a second on a single core for each block. It's 900KB for a full block. The only reason it would take a long time is a particular client using CPUs extremely inefficiently and leaving them idle most of the time.