Community production coordinator Tait Watson, took to the forums today (Monday) to confirm some information that was already known for the most part.
In detail Watson, highlighted that:
There will be no downtime or patch tomorrow for the launch of Preferred Access as we will just be flipping on access for those accounts.
The Constable’s Stronghold Pack will be released tomorrow at roughly 11AM CDT (4PM GMT).
It’s also worth mentioning that tomorrow is the day when preferred access members get access to the Galactic Strongholds expansion so expect to see additional people logging in to check out the latest SWToR expansion.