Sure, that's fine if all you want is to measure the time from the big bang until the last matter in the universe has evaporated into photon soup. But what if you want the time until those photons are evenly distributed? An article I read a while back estimated that duration as 10^10^78 years, which is absolutely mindboggling and remains the largest number I have ever seen with a real-world physical application.

(It may never happen, though; according to Wikipedia, random quantum fluctuations may be sufficient to produce another Big Bang in a mere 10^10^56 years.)