Just announced at the PlayStation Experience keynote. From 12pm PST (which is 4am Perth time this morning) to 6pm PST the next day dunno! As of this edit (1pm Monday WST and way past 6pm PST), the games are still free. Will update if they announce anything more specific for AU. (Apologies if I don't - staying up to watch and I haven't slept yet.)
Applies worldwide, according to EA and Sony: https://twitter.com/PlayStation/status/541307020414947328
UPDATE: Now live on the US PSN store, so if you have a US PSN account you can grab the games now. Hopefully it goes live for the AU Store soon.
UPDATE 2: NOW LIVE FOR AU. I'M GOING TO SLEEP NOW.
PvZ
NFS
Mirror's Edge
US PSN links thanks to BluBoy:
PS VITA - Need for speed: Most wanted
Playstation 4 - Plants vs Zombies: Garden Warfare
Playstation 3 - Mirrors Edge
Remember you do not need the consoles to download the game! Just add it to your cart and check out.
The games will be yours to keep for as long as you have the PSN account from which you downloaded.
Starts 7am AEST