I find this issue rather unique. I have a 2007 G35 S Sedan 6MT.

When it's warm/hot (75 degrees +)outside, I have to hit the Start button multiple times before it will turn over and start. However, when it is cool/cold outside (74 degree -) it will start up with a simple 1 touch.

To make clear when I hit the button without the clutch engaged it goes to ACC, everything works. Nav, radio.
When I hit the button with the clutch engaged and the times it doesn't start up, everything else comes on, A/C, lights, radio, etc.

Eventually it does start up, I have not yet been left stranded. However, I need to get this fixed before I do.

Please let me know if you need any further information.

 

Battery going out? how many miles? What have you recently maintained?
If you assumed we would ask for more info you should have given it, ha!

 

This could simply be that the switch makes better contact when it's colder. Next time it's warm, try being very diligent about pushing clutch pedal in all the way, wait a second or two, then press the button once and hold it firmly for a second or so. If it's simply a contact issue due to some subtle expansion and contraction on the contacts, then a casual 'stab' of the button might not quite make it. Give it a shot and see if it still repeats your symptoms.

EDIT: on second thought, it could also be poor contact on the clutch interlock switch down at the pedal.

 

Sounds like your push button is going bad. I've replaced 3 in the last few months for the same exact issue. When it gets really bad it is hard to turn the car off once it is running. Hope this helps