Since privacy is an issue at my place, and hogging the bathroom for too long will also cause issues, I have learned a method to warm up efficiently. It may not work for everyone, but is perfect for me.
I perform my PE routine in the shower. Prior to taking a shower, I run hot water in the sink and get a wash rag nice and hot, squeezing excess water. I wrap it around my penis, and standing at the counter, I hold the wrap in place by leaning against the counter top. My hands are then free to do other things. Brush my teeth, wash my face, shave, etc. When the wrap cools, I put the hot water on and reheat it, and continue. My pre shower routine lasts about 10 minutes, but when I get in the shower I let the water warm up my penis for an additional few minutes while I wash my hair. I perform my PE routine, get clean and get out.
After my shower, I warm down the same way as the warm up. I do this while blow drying my hair, etc.