I am writing a novel with the basic Wizard of Oz, Alice in Wonderland or the Matrix if you want structure. The novel begins in perfect modern day, and at some point in a very sharp way takes a turn for fantasy.  

Right now Kansas currently takes up about 4000 words and aside from an end paragraph is the entire first chapter. There are virtually no magical elements in it. We meet the characters and find out what are their mundane daily lives before everything is subverted. By mundane I try to not mean boring. One is tied up with a crime family, and the other one is struggling with drug addiction.  

The feedback I am seeing from my test readers is that because the book is in the fantasy genre they expect fantasy. They want foreshadowing to the fact that there is magic in this world. 

My question is, is this something that the modern reader needs? Do we have to put early fantasy elements to keep readers interested? How long can a standard length novel spend in the modern day world before it has to show magic? I am assuming that the normal world action is interesting if the reader just did not know the book was in the fantasy section.