Minimum Boat Preparation Time? (going offshore)

I have an interesting question - what is the minimum time you would plan to allow from day of boat purchase to day of departure for a 6 month cruising trip including an Atlantic crossing?

Now, this question is like 'how long is a piece of string?' so if you don't mind me sharing my scenario I can narrow it down for you -
My wife and I have been researching boats for years and have a shortlist of suitable yachts we've decided on, and from what I can see online we can afford to buy a yacht in 'sound' condition (probably Florida) that won't require a major overhaul.

I ask because we are working back from the Atlantic hurricane season for the ocean crossing. I'm trying to work out a rough cut-off date to fly to the States to buy a yacht, before we have to delay another year. Once we've found our yacht we will be working full-time on preparing the yacht for the cruise.

Here's an example yacht otherwise my question is too difficult to answer - let's say a mid 80s Tartan 37 that's had regular refits and is in 'good' condition. No major structural concerns, nor deck leaks, and let's say the engine was overhauled in the last 5 years, hull has been repainted, and most equipment is in servicable condition. Let's say for this example we'll replace her standing rigging for an ocean crossing and have the through hulls checked and serviced, a new mainsail and Genoa, new batteries, engine service, and have to find and purchase a few extra bits and pieces for a 6mth cruise - lee clothes, additional anchors, new bimini, and minor bits and pieces.

with this example in mind -
1. What is the rough minimum time (weeks/months) you would allow to be comfortable with your plans? (purchase to departure)
2. What is the bare minimum time (weeks/months) you think this is do-able in? (or before plans just aren't smart!)

I know no one can give me an accurate answer without seeing a specific boat, but for the sake of rough project planning I'm interesting in seeing the range of answers from seasoned cruisers (eg. 3-4wks, 3 months? 6 months??, etc).

I will value your input highly thank you.. We are currently in decent jobs in Oz so the later we leave it to fly to the States the more cash we'll have for our trip (but my wife and badly don't want to put off our trip, we've waited ages already!).