How long do I put olive Oil in my hair for if I want to treat it and for it to promote growth?

hey everyone , so my name is Jess and Im having a formal soon and Iam hoping to grow my hair really long , I ve heard that by putting Olive oil in your hair helps promte growth and makes it healther , is this true and if true how long do you leave it in your hair overnight , or do u leave it in then wash it out with shampoo or condition ?? Thanks Guys appreciate it greatly xox