Time zone for sellers and buyers

we need to default to a local time zone for sellers and buyers. For example a london based seller and buyer doesn't need to see options for world time zones when he is setting up his profile. We should have an ability to select time zone via admin panel that we would like to display on our marketplace for our buyers and seller to select while setting up this profile. 

So for marketplace in UK should only show UK timezones not the US or Asian time zone options. This will clear the confusion for our buyers and sellers while setting up profiles.