X is your cookie. When adding value to X (initilization) set another cookie (lets call it Y) with current date in milliseconds. When you want to calculate time of X, you can use value of Y and substract it from current date. You will get how much time passed after initialization of X cookie.
Security Issue: Insecure Protocol
An application does not use a secure protocol, such as HTTPS, which makes the session cookie prone to network eavesdropping.
The following security issues could apply if you do not perform the tasks presented in this document.
Security Issue: Shared Session Cookies
All applications share the same HTTP or HTTPS session cookie. This shared session-cookie scenario enables hackers to intervene by using an untrusted application to hijack the session cookie. With the hijacked session cookie, the untrusted application can impersonate the user and access protected web resources.
Security Issue: A Less Secure Application
If a single “less secure” application is hacked, the security of the entire infrastructure is compromised.
Security Issue: Access to User Profile Attributes
The untrusted application can use the session cookie to obtain and possibly modify the profile attributes of the user. If the user has administrative privileges, the application could do much more damage.