The way it was explained to me was that, when you start DA:I it will ask you to log in to your Origin account (through the game, not your internet browser). When you do that, it will ask if you want to import a custom World State. Say yes and, provided you have created one (and hit the export button in the Keep), the game will import it and link your PSN account to Origin automatically.
Being a technophobe, I was reluctant to leave it until launch day and I wanted to have my PSN and Origin accounts linked in advance. I was told to do this:
- download and install the "Origin Client"
- Click the "Add friends" tab
- this will present you with a panel containing options to link your PSN and/or XBL accounts.
I did this and my Origin account connected to PSN pretty much instantly. I'm in the UK so I can't say yet whether that has made importing my World State any easier, but I do feel far more comfortable knowing that my accounts are already linked up.
So, in short, you probably can just wait until Friday and let it all happen automatically. But, if you want to link your accounts now, the above steps really do only take a few minutes.