Pushka, from the tone of your contribution you may be one of our amazing 'on the spot' reporters. Nothing beats this.
Funnily enough, I had checked this flight only 45 minutes ago: it was showing as punctual.
The QF website claims that this 1220 MEL - SIN will instead depart at 1400, so in the scheme of things it is not a huge delay, certainly not like what passengers on today's (26 December) QF19 from SYD to MNL (see above) are facing. Would QF obtain a 'replacement' A330 (A332) from a domestic flight? If I am not mistaken, it would not normally have a spare A333 sitting around in MEL.
Please keep us updated. I assume you are in the lounge.
How long does a cracked windscreen typically take to replace? Can this usually be achieved while an aircraft is parked at an airport gate, or does it have to be towed to either a hangar or elsewhere on the airfield?