One of my students was worried that it took her 4 hours to write a band 7 essay for homework.
In my opinion, spending 4 hours to write an essay is a good idea. This kind of hard work leads to great results! The important thing is to be able to write your first band 7 essay. At first it might take you 4 hours, but you will get faster with practice.
PS. The student I mentioned got a band 7 in her exam about 6 weeks later!