What is the legal life span of pct invention patent and pct utility model patent respectively?

First, PCT patents do not distinguish between inventions and utility models before entering the patent offices of specific countries for examination.

Secondly, according to you, "life span" may refer to the time of the first phase of PCT (that is, the international phase), which can usually be considered as 30 months, counting from the first application. However, different countries may stipulate a grace period of one month or more according to their own laws, in which case the "life span" will be longer.