I think you should swap under the following conditions:
1. The product no longer works on your skin as it should.
2. You can no longer afford the product.
3. You no longer need the product.
4. The product formulation has changed, and you don't like the new formulation.
5. You have adverse effects from product use, such as rash, redness, or acne.
6. You're bored.
So all in all, there is no set time to be with a product. I've had products that I've used for years and others that I've thrown out after the first time I used them. It's up to you to decide.
1. The product no longer works on your skin as it should.
2. You can no longer afford the product.
3. You no longer need the product.
4. The product formulation has changed, and you don't like the new formulation.
5. You have adverse effects from product use, such as rash, redness, or acne.
6. You're bored.
So all in all, there is no set time to be with a product. I've had products that I've used for years and others that I've thrown out after the first time I used them. It's up to you to decide.