The normal time it takes for Google to reply on Adsense applications varies by the location of the applicant. Also, the required age of your website also depends on your location.
Usually, in the worst cases, you should hear back from Google within 30-45 days but then there have been cases where Google hasn't replied for months together.
And by your question, if you mean that you have received a reply and the reply is that Google won't approve you, then they would have mentioned the general reason in their email.
One very common reason for rejection is the use of duplicate content on your website.