1.There is no such thing as Instant approval from Google.
2. First you need to apply for Google Adsense.
3. Wait for the response from Google - first they will review your site and give you an equivalent of temporary approval.
4. They will monitor/review your site for a limited time and then may or may not give final approval
(From September Google has been following this two step approval process for Adsense approval).
Your final approval depends on :
1. How much content you have and
2. The quality of the content
3. Adherence to Google TOS
Read the Google Adsense application steps, its TOS in detail to understand the whole process in detail. Good Luck.