It's hard to find authoritative links, but by all indications I have ever seen or read, implosion is nearly instant. The pressure differential is large. As soo

It's hard to find authoritative links, but by all indications I have ever seen or read, implosion is nearly instant. The pressure differential is large. As soon as the hull gives way it's essentially like a bomb explosion in reverse. I suppose it's possible that some external piece of the sub might have exploded and left the sub itself stranded but intact on the ocean floor. However, it seems that's not what happened -- pieces of the sub's main body were part of the floating debris field. It provides some level of comfort to know that the passenger's demise was likely instant as opposed to slow and terrifying.