Now is a good time. Or you could decide what you would pay in monthly payments and start making those payments religiously into a bank account while you continue to drive this car without putting a dime into it except for gas and oil changes until it breaks down, at which point you then take that money and buy a new car, and if from a lot, get that car to the dealership however you can and accept whatever trade-in they'll give you for it, and if not from a lot, put it on Craigslist or whatever and sell it for best offer.
By the way, if it weren't rusting and hit, I'd say go ahead and fix it because 115,000 miles and 9 years isn't really so much on a car these days, but when on top of what's mechanically wrong with it, it's damaged and rusting, its not a huge amount of miles and not a huge amount of age really matters. It's pretty much lost its value.
By the way, replacing CV joints isn't a huge expense, sort of medium, but that AC compressor is. Fixing the AC will cost you a couple thousand. Nobody's going to spend very much money on a car, even one with only 115,000 miles, if it doesn't have working AC, and it doesn't sound like it's a car that's worth dropping $2,000 to $3,000 into fix the AC, not when it's also rusty, damaged, and needs $500 or so in repairs on one CV joint, meaning another $500 or so for the other one is right around the corner.
That said, you can drive around a rusty, banged up beater with the windows down and clunky CV joints for a really long time. It's not unsafe. You could easily get another year or two, or maybe even more, out of that car before anything goes so wrong with it that you can't drive it anymore. And if you're banking car payments that you' would've been making on a different car during that time, when it comes time that you do need to replace that car, you'll have saved a huge amount in depreciation of whatever car you would've bought and also actually have the money to get a nice car, one that won't be only barely better than the one you have now.