I agree with maybe moving to end of Q1 if possible. The challenge really depends on the complexity of your operation, leadership buy-in, and how much time you are able to dedicate to it.
I've now implemented SQF for 4 separate businesses as QA Manager. The most recent one I started with almost nothing (including no HACCP plan as almost all of the previous documentation was lost due to an external drive failure - that was "fun"), and wrote everything (converting many from previously existing templates from a FS Consultant) in 2 months, and then was audited with about 3 weeks of solid records after that. (98%)
The one previous to that was about 5 months to implement in a large but new RTE operation and a great Corporate QA person doing most of the writing - that was a hot mess but we passed with a 97%. (I've implemented SQF in 2 facilities this year)
The only reason that succeeded is because a) the owner told everyone to do whatever I said, b) jumped on whatever I asked, and c) is a new, extremely well designed and clean facility with a simple process and one formulation of low risk product for further processing and a shared allergen profile with about 5 ingredients and d) I was able to focus almost solely on implementation every day. 0/10, do not recommend if you have anxiety and/or enjoy time outside of work.
They removed the 3 month requirement of records, so technically you can push your true implementation date pretty close to your audit if you have any records you won't have SQF ready. If you do this: You can use the records you have on lockdown as a good way to help demonstrate to the auditor you have effective implementation and a culture/commitment to maintain it, just maybe a few pieces weren't ready until close to the audit.
Recommendations: Get a 3rd party Gap Assessment, it's a good investment. Plus if you expect to have a lot of arguing from people set in their ways, it's a really good way to start off right and set the tone from the get go. Make sure the owner/senior site manager is involved in the gap assessment for a period and have at least one key person from production management come with for the full gap assessment. There are things you may think you're meeting that the consultant will be able to identify you're not, and things you think aren't meeting the code that you are. (It's gotten better, but I swear SQF code still has the tendency to mean one thing but write another in places).
It goes way better if your senior site manager truly buys in. If you don't have that, it's a painful slog and the most likely cause of failure. Management/Senior site manager needs to show up to the opening meeting, but if they're invested they wouldn't want to miss it. Keep them updated.
And finally I always spent a lot of time training our production personnel what SQF means (weekly pre-shift meetings). (Like what it really means - we are getting SQF certification because we want to make Safe, Quality Food.) Repeating that stuff over and over again is more powerful than it seems, and it helps connect WHY all of these changes are suddenly occurring. The best programs in the world mean nothing if your front line doesn't follow them.
Good luck!