An application for labor certification must be filed within 180 days from the start of recruitment, so that's about 6 months. But that is the maximum period. The minimum period is just over 60 days, to account for the required 30-day job order plus the subsequent 30-day cooling off period. Typically, an employer can file the application from 65 to 90 days after starting the recruitment, and up to 180 days after starting the recuitment.
You really should consult with an immigration lawyer. If you need to ask this question, there are a hundered other questions you do not even know to ask which will arise later. Do not attempt to prepare and file a Labor Certaification on your own. Consult qualified legal counsel for assistance. This is a VERY complex process that MUST be done RIGHT!