Random command QUESTIONS - HTML

i have a big problem for long time,

I need to do this -

I want to display two things on random - X and Y for examply, so if a user enteres my website he can see X or Y on random, and it will change every minute to X or Y,

this task is easy, i can do it to.

The thing i wanna do is, EACH USER that enters my website will see the same THING, so if user 1, 2 and 3 are on my website each one of them sees X and when it changes they see the same thing,

and another thing, when the user reloads the page, the value will not change, until the time came and it changes after one minute ( NOT 1 MINUTE AFTER HE LOADED THE PAGE, but 1 minute after the function did RANDOM )

Please help!