Why can't I put food on the pan while the stove is heating up?
There is a simple fact which many intermediate cooks don't seem to realize: 

The rate at which you pump heat into your food has a huge influence on what the end result tastes like. 

So, if you put food into a cold pan, and it gets heated slowly, you end up with a different result than if you throw it into a hot pan that transmits a lot of heat into the food at once. 

Both techniques have their place in the kitchen, but the "heat quickly" one usually produces results which the majority of people like - vegetables stay firmer, doughy foods get a nice crust, sticky things release easily, etc. So it is used more often. And if you want good results, I'd suggest to stick with your recipe and use a heated or cold pan as it directs you.