from what i have seen, private jets generaly get put to bed after a days work. however commercial jets tend not to as unless they are parked in the middle of the airfield, they and protected by the terminal buildings etc. they dont realy spend that much time on the ground for someone to get the ladders out and get all the covers on. im cant remember where i heard it, but in the early part of my training one of my instructors told me that during the average aircraft spends about 70-80% of its lifespan in the air.
some airlines have a 25 minute turn around time, and others 4 hours. even if an aircraft is on the ground for the night, generaly it will be back in the air within say 6-10 hours. this is also the time that work is carried out by the tech guys as it causes less disruption the the flights the aircraft has to do the following day.