Hi Darren,
Rob mentions the timing of when the GRS is visible. Yes, I agree with Rob that a program like Stellarium helps in determining when the GRS is visible. Or you can just roll the dice and have a ping whenever you can get your scope out. You have a 50/50 chance any time. The transit of the moon's shadows are very spectacular too. And the skirt across the disk quite quickly too. Again, Stellarium can help determine when a transit will happen, and of which of the Jovian moons.
Observing tips: Your 9mm eyepiece should be able to show you the GRS. The only hinderance will be atmospheric turbulance, which is always greatest close to the horizon, but at the 133X your 9mm will give you, it won't be too bad (can vary though). Light pollution is not a problem with the Moon or planets. They are all bright enough to view comfortably from inner Sydney! I pretty much limit all my observing and sketching from home to the Moon and planets for this reason. Uranus is easy to spot in binos from Sydney, and Neptune too, but more of a challenge and best in a scope.
The only thing about the GRS is that it is not as prominent as it used to be. Its famous cherry red colour has paled to a salmon pink, making it more of a challenge to pick out from the glare of the disk. Take your time with it as it won't stick out as you might expect. Colour filters can help spot it, along with different cloud features of the Jovian atmosphere. But before you go rushing out to buy any filters, be aware that you will use them rarely, and you are best to get just two or three. Which coloured filters? Up to you - sorry if it seems like a cop out, but you need to read up on them first and determine what best suits you. Remember, these coloured filters I'm talking about are not the various nebula filters, which you will use more frequently, and can also be used with the planets.
Here is a very good site to inform yourself about filters, colour and nebula, and what they are best suited for:
Lumicon nebula and colour filters
Happy hunting,
Mental.