This is a terrible idea. Stability and gradual, generally understandable, evolution in response to real world conditions are positive attributes of the current precedent-based system that has grown out of the common law.
Plenty of laws are relevant only to a specific point in time, but they rarely, if ever, get repealed.
Take the US Chicken Tax. It was put in place in the 60s to deal with economic concerns with France and West Germany at the time (which no longer exists as such!). Why shouldn't it have been given an expiration date? Instead, it remains in perpetuity, with its provisions twisted every few years to suit the interests of auto industry lobbyists. This is perverse.
But not all laws should expire. Having, say, the crime of murder expire would be quite unhelpful.
I'm pretty sure that laws like that one would be renewed before expiration anyway -- and the current context would allow re-evaluation of penalty as well, which might be something useful to reconsider every couple of decades.