Is it possible to replace browser timezone information with router tools?

Question

Computer networks

Given: A
client computer connected to the Internet via a router. In the role of a router - a linux server with 2 network cards. The OS of the client and its browser are generally not defined (that is, they can be any).
Task: when going to an arbitrary site using the router, replace information about the timezone if the site tries to do this.
Personally, it seems to me the task is almost unrealistic. Taking into account the fact that the site can determine the timezone using a js script, which will be obfuscated according to a previously unknown algorithm. But maybe there's something I don't know? We consider options for using the site HTTP and HTTPS.

Answer 1

Well, you can, for example, implement Javascript, which will do dark deeds. But I'm not sure about the feasibility of the method. Not sure if JS allows you to intercept date functions. And there is a ready-made functional for modifying pages on the fly.

Answer 2

The only way for the server to get the client's current timezone is with Javascript

var offset = new Date().getTimezoneOffset();

In the case of HTTP traffic, you can try to implement a script that overrides this function (I can’t say for sure). But for this, the router must parse the traffic up to L7, which is quite resource-intensive and not trivial. As an example, run through a proxy and change the content.
In the case of HTTPS, a dead number. The traffic will be decrypted directly on the client and will be completely inaccessible to the router.