Definitely MUCH more then 30 seconds. Unless you want a bugged and SMP-infunctional Luminator. 1-2 hours of total work, most likely.
Why is it more work? All it is is an additional server side stored integer which counts down in the tile entity on tick. Having a delay before a luminator can reactivate will be a partial bugfix....until the awesomeness you guys are coding can be released. Whenever the tile switches from Luminator off to luminator on it forces a block update on the client and a lighting update so a delay on the server so I dont see why if it works in single player why it wont in multiplayer.
This. There's still a client and server component, though the client one of 1.3 is much smaller then the 1.2.5, consisting of player control and rendering only (and a few minor parts). The only advantage for developement is the fact you can fully test "SMP" in a local SSP environment.