My MY RWD begun preconditioning the battery for a supercharger stop while I was still in Glasgow heading to Fort William. Took 2 hours with no traffic but I thought it was pretty early.
I find that it stops and starts preconditioning as required (or as the car believes it's required). It doesn't necessarily use power preconditioning for the entire period. I would suggest that people let their car do what it thinks is best on a few trips to see how it works before trying to to second guess the charging strategy. More often than not the car does a good job and ensures that you get fast charges whilst protecting the battery (by maintaining optimum temperatures). Once you have a good handle on how it goes then you can experiment with situation-specific scenarios where you know something that the car doesn't.