How to Set Default date-time GMT -5 UM5?

[eluser]Unknown[/eluser]
Hi,
I like know How to Set Default date-time GMT -5 UM5?

I have a problem because when i tried to save a date like date("y-m-d H:i") this return the server date-time and not the user date-time, and becuase all users are in GMT -5, i need to make the Default date-time GMT -5 UM5, please help me!!