Harm in "ready" mode?

There is no upper limit other than that dictated by the fuel tank capacity (i.e., running out of gasoline.)

 

Could be days or even weeks then

 

Well you will be putting more wear and tear on alot of parts. But who knows if it will shorten the life of the car. But you may have to replace some parts sooner like the ac compressor, Fuel pump things like that. But i wouldn't worry at least your not burnning gas the whole time your car is just sitting there.

 

There's nothing "premature" about it. Cars are meant to be used. Far worse to be sitting in ACC or IG-ON, because they will kill one or other of the batteries.

 

I suspect the most likely "harm" from repeatedly and frequently having
the car in "Ready" for extended periods would be early failure of the
DC-to-DC converter coolant pump. As Patrick, Hobbit, and others have
noted, it runs whenever the car is in "Ready."

While the pump's probable service life is typically expressed in "miles
driven" -- usually given as 100k miles, but failures have been reported at
~65k miles -- it's life would be more properly expressed in "hours in
'Ready.' "

So let's see, 100k miles at say 30 MPH overall average -- gotta' count
time stopped at lights, etc. -- would be equal about 3333.33 hours.

How many hours do you think you will spend sitting stopped with the
car in "Ready?"

 

What do you mean by extended periods? Hours or 15min?
2 of my kids are in dance and between 2 2007 I leave my teen in the car doing homework with the AC on low for 45min twice a week (so calif area hot). Not had any problems. It works very nicely not running the gas engine constantly. As with cars, something could break tomorrow or never.
Before that constant bumper to bumper traffic (just about idling going no where), no problems there either.
Do regular maintenance and the mechanical things will last longer. Of course idling saves on tire wear, brakes, lights, excess engine wear at high speeds, switches, washer fluid and all kinds of other things while not moving.

 

Idling is usually a concern in big engine cars from what I recall. Having the engine running with and AC on and not having any air movement on the engine would harm them. I dont think it is even remotely an issue with a prius. In fact many people have camped in their priuses and kept them on overnight for a nice 70degree slumber party

 

Now you're worrying me!

 

Dont warry, replace your 2010 HEV with a new PHV when it is available, you will get 5000 pounds grant from your government I heard!