My 2005 Ford falcon takes a while to kick over when I turn the ignition on. What's the deal?

There could be any number of faults. You'll need to get a mechanic to plug in an OBD code reader to the engine management system and then it will tell you where to start looking. At the end of the day, all an engine needs to run is spark, fuel and compression. This could be a bad fuel relay or pump, a bad sensor or ignition module, the timing chain/belt could've blown, even the engine management module etc. Get the fault codes and it'll eliminate the guesswork.

Perhaps the fuel filter is clogged. They are inexpensive and easy to change. Sounds like a 'fuel delivery' problem, not electrical or other issue.

check the battery in the fob as it may not be engaging the immobiliser.

Have you changed the fuel filter?. Have a fully charged battery if the cranking voltage drops below 10 volts the computer can't work and it wont start.

Its either no spark or no gas. Remove the fuel line and carefully crank it over..are you getting any fuel? If not possibly clogged fuel filter or bad fuel pump. If yes, are the spark plugs firing. Remove number one plug lead hold close to any metal surface on engine, crank over ..spark there..strong or weak spark? No spark check coil and associated parts.

Why are you pouring hot water on the ECU? I would be checking the spark plugs first

put a new ignition switch in the car

check the immobilizer for operation
unfortunately the coil packs on the falcons are subject to failure so you may have to remove and have them tested

The fuel pressure relay in the engine is not working or the fuel pressure relay is not working .
Try to replace the fuel pressure relay or soleniod in the engine area.

IF this does not work , Check the timing of the engine.