[citation needed]. I can't find any information to verify this.
So, if it draws about a kW in use, that means that if you use it for less than 130 seconds per day, or just under 2 minutes, you'll actually use more power on standby than on cooking / heating.
I think I use my microwave more than 2 mins each day, but there are days I don't use it at all, so I'm not sure how it would even out.