changing default time ubuntu prompts for password when computer sitting idle?

[Hank Smith]

Hello where do I go in ubuntu to change the default time ubuntu prompts 
u to inter in password when computer sitting idle?
I don't like the amount of time it is set to when doing stuff each time 
when I come back after 3 minutes or so I have to inter in my password I 
want to change the default time on this
how do I do this?
Hank


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