Well if you work next to a shop that sells computers, and they just happen to have in stock, a computer that meets your needs, then the delay time is about the same as the time it takes you to get to the shop, buy it, and get back...
Or you could have a room full of computers sitting around just waiting for the next failure. Just how far down the rabbit hole do you wish to go?
How about having a spare machine out in storage, in case your current machine/s fail?
Really? the Answer to your question is the same as asking "how long is a piece of string"
Yeah, that would work, but then if critters got in to the paper and ate holes through it, then your "paper" backup has now failed... or what happened if you had a water leak? Same result, paper ruined.
Fair enough, but make sure you have the vet on standby to extract the "backup" from the dog!