This isn't contained to the group page. Every timestamp on ROBLOX between the forums, group pages, game pages and everything else runs on a different timezone.
It's not a ducttape fix to fix timezones across the website properly. It's ignoring the problem because it's not "significant" enough.
And given this issue has been around since most of ROBLOX's inception I seriously doubt that's a reason why they aren't going to do it