As per my knowledge and research, the maximum CPU time on the salesforce servers is 10,000 milliseconds (Synchronous limit) and 60,000 milliseconds (Asynchronous limit). We can’t exceed this limit. But an important point to note here is to know that CPU time will vary when running the same code over and over again. The CPU time vary by as much as 25% from one request to the next. Salesforce don’t not give any information on how much of a variation that can be expected.