what is the server security certification is not yet valid

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Hi, friends. Today I try to use open my googel mails, But the red squar show out " The server security certification is not yet valid" , What does this mean, I have not idea about it, Now I can not open my google mails box, Is it means google server down or my laptop server problem,May i know if you have this kind of experience? Would you please advise, Thank you ..