Allowing a wine to "breathe" is simply a process of exposing it to air for a period of time before serving. Exposing wine to air for a short time, or allowing it to oxidize, can help soften flavors and release aromas in a way similar to swirling the wine in your glass.
Now when it comes to the amount of time red wine needs for aeration depends on the age of the wine. Young red wines, usually those under 8 years old, are strong in tannic acid and require 1 to 2 hours to aerate. Mature red wines, generally those over 8 years old, are mellow and need to “breathe" for approximately 30 minutes, if at all. Open, Enjoy