[autobonrun]

I normally just clean during the winter months. The time to do the rejuvenator oil softening is during the summer. Typically, I'll saturate the leather and let it sit with the windows up. Sometimes it's so hot in my garage during the summer I don't even put the car outside. I've never even considered doing it during the winter. Maybe it will work; don't know.

I'm not sure why you are using the prepping agent. Are you redying your seats or just trying to soften and clean them? The prepping agent is only needed prior to a redye. If you just softening, I'd keep all the original dye I could on the leather. As others have said, use heat to open up the pores.

Edit:

I take back what I said. I read the instructions on their site again, and the prepping agent can be used to open up the pores if the leather is not absorbing. I think you will still get better results however in the summer.