The experimental timezone feature enables the Timezone setting in the Account Settings and a timezone is automatically assigned in the next active session.
When hidden (i.e disabled), it will set the timezone automatically from the local machine time. For example, I am located in Malaysia and the timezone that I have on my machine is GMT+8. So, the timestamp on my client will be similar to it.
When enabled, it will display the following in which I can decide to set it automatically or I have the ability to choose a different timezone:
When the Set automatically is unchecked, you will be able to choose the timezone manually:
To your point, there is no direct way of forcing the timezone since it is on a client level and the custom build is limited to certain features only.
Is there any particular as to forcing timezones for all the users since it might cause confusion for users who work in different continents?