As others have said, this isn't really about market timing, it's about allocation. If you expect to need the money soon, it should be allocated to a stable investment.
There are some ways to lock in your capital gains now, but realize the gain (for tax purposes) next year.
Let's say that you have a S&P 500 index ETF and the price per share is currently $100. When you buy a put you pay $x for the right to sell that ETF for $100 at a specified date in the future*... let's say a year to keep it simple.
...but that's not one of them. The IRS will call that a 'constructive sale' and force you to take the profit, as a short term gain , THIS year if you buy puts which are in or at the money.
One of the ways to do it is with a collar... you would basically sell covered calls at a price above the current market price, and use the money to buy puts below the market price. This establishes a floor on your losses should the stock drop significantly, and also a ceiling on your profits should the stock rise significantly. To avoid the constructive sale rules, the puts and calls need to have a spread of about 20% of the stock price, and both of them should be out of the money.
Another is with a non-constructive short sale... in order to accomplish this, you
1) short the stock now;
2) close out the short within the first 30 days of next year;
3) continue to hold the stock, unprotected, for at least another 60 days, then
4) sell the stock.
At this late point in the year, this probably doesn't offer you much advantage.
I intentionally haven't provided a lot of detail here, just enough to give you some keys to do more research (and/or cosult a tax professional) on your own.