Does the rule limiting encounter powers to 5 minutes actually exist?

[Turtlejay]

Just like the title says. I see this quoted as truth all the time, but I do not recall there being an explicit rule that says all encounter effects last only 5 minutes. Does it exist? If so, where?

Thanks,
Jay

 

[Mort_Q]

See Duration, PHB 58.

 

[Turtlejay]

Thanks. I see this said all the time, but almost never with any reference. I haven't read the PHB cover to cover since it came out. . .

Jay