Strange Engine Startup

[AUSVX]

Hey guys, hopefully this is an easy fix.

When I start the car from cold in the morning (and I mean DAM cold).. My car starts without a problem whatsoever.

When I've been driving and the engine is completely hot (say for example over half an hour of driving) and I turn the car off and get back to it a couple of minutes later, it starts really well, like you just need to turn the key for a very very short period of time.

BUT!!! when the engine is completely warmed up, and I turn it off and go and start the car anywhere between 1 and nearly 3 hours later, I'm holding the key down for a good 6 seconds just waiting for the bloody thing to start up!!

Here's how I start my car up most of the time... I turn the key to accessories and leave it there for about 15 seconds until everything seems to be ready and settled and then I start it.

My battery is in good condition, and I have no faults according to the flicking engine diagnostics

Any suggestions??
Thanks, Jordan.