Handling the GMT time offset (for site visitors from different regions)

[adrianTNT]

Hello, I have some questions about dates/time ...

 

I have a site where registered users will receive messages, I want to include the date/time with that message.

I am not sure what is best way to do this, so I am recording the GMT hours offset from users input (from receivers), but then I saw that the hours offset from the GMT is different in different seasons of the year, so how do I detect correct local time for the message receiver? Is it something like a database with start-end time of daylight savings hour adjustment or how is this done?