I believe that, in the scene, Kate's phrase was a Hyperbole wherein her saying, "That was, like, three seconds," isn't a literal statement to Jim's 'quick death' but rather her exaggerated, and sarcastic, response to how quickly he 'died'.
For example, a similar use of this kind of phrase is often used by the speaker as a sarcastic, or ironic, reply to something that subverted his/her expectations (much like how a straightman responds to the punchline to a joke).
Picture two individuals: Tom and Tim. Tom asks Tim to go out and get him a coffee, expecting Tim will be gone for 10+ minutes. Tim leaves only to come back less than 5 minutes later with Tom's coffee. Tom, surprised, exclaims, "Dude! That was, like, three seconds!"
[Tom is surprised how quick Tim was to deliver a coffee]
Alternatively: Tom asks Tim to make a pot of coffee in the next room. Tim leaves to the room to make coffee while Tom waits. However, Tom remembers (less than a minute later) he left his phone in that room as well and enters to ask Tim to pass it to him. However, upon entering the room, Tom sees that Tim had completely destroyed the room with spilled coffee grounds, creating a mess that seems impossible to make given the short amount of time passed. Tom blurts out, "Dude, it's been, like, three seconds."
[Tom is in utter disbelief how Tim managed to make such a mess in a short amount of time]