There are many variables that can affect a home and a paint job. Most are beyond the control of the painting contractor; these include customer damage or abuse, customer supplied paint, roof leaks, etc. You get the point. The aspects of the job under the contractors control is the details that make up the labor of the job according to the contract and any supplied materials.
It is during this time that any defects in workmanship will appear. Longer times are used by painters as a sales clincher to entice you to sign the contract. Most interior paint jobs don’t require a warranty as this type of painting generally lasts for many years, even decades.
The real value of a professional paint job is the painter. Even with the most expensive primer and paint, experience is still the most important. With experience there is detail. Good results are in the details of the job, how it’s performed, and the types of products used.