Should I reset the ECU while the engine is hot or cold?
What should I do after reset the ECU? Let it idle for minutes or hit the road?

Any help would be appreciated.

i dont think the temperature would matter much, but just incase i might start it in a garage. everytime you reset it im told you should let it idle for a couple minutes, then get going. i guess it has to readjust. that may be old wives tales but i do it any how

Can I ask why you're resetting it?

I had reset it couple times and I drive the car immediately afterward. I'd found the car is running rich gas mixture. and I smell gasoline from the back of the car at cold start up.

after you reset the ECU the emissions need to re calibrate...
the exhast needs to be hot so that the sensors by the cat. read properly...
but as it a learning ecu it should adjust either way....

What a Pro. thanks for your info.

yeah every time you reset it just learns quicker than if u change something and do not reset. it( the ecu) has a learning curve and will adjust to your driving style for best perf and economy. (to an extent . it's factory you can't ask for too much)