My '13 F30 is my first BMW, and my first car with lots of cool modern technology features (my old car was an '03 Dodge Stratus MT).
My heated seat takes a few minutes. Honestly, I'm underwhelmed with it (I also got it as a standalone without the cold weather package and heated steering wheel FWIW). It takes a long time to warm up, at which point the vents are sufficiently warmed up to not really need the seat. Plus, once it's fully warmed up, it's HOT, and so I basically have to reduce it to 1 bar anyway.
Next time I'm in the market for a car, if I'm at the point of trying to trim costs, heated seats are probably one of the first things that will get ditched.