I am working on website which has session timeout after 10 mins. From the website I am able to capture the time at which it logged in (Eg 06:16). This time is stored in string variable. I want to compare this time with the system time. How can I do

I am working on website which has session timeout after 10 mins. From the website I am able to capture the time at which it logged in (Eg 06:16). This time is stored in string variable. I want to compare this time with the system time. How can I do it?