The LCA must be filed by the petitioner to show that (1) at least the prevailing wage of the occupation for which the employee is being hired will be provided to the employee and (2) the working conditions provided to the employee is such that it will not adversely affect the working conditions of other workers that are similarly situated.
Because the LCA cannot be filed more than six months before the employment start date, complex issues arise for H-1B petitions for a couple of reasons. First, as the H-1B effective date is always October 1 and you cannot file for LCA until April 1, but you have to submit the H-1B petition on April 1 to beat the quota, what do you do to juggle these dates? Second, it takes a while for the DOL to certify the LCA, would USCIS consider H-1B petitions without a certified LCA? And, what do you put as the start and end dates of the employment on the LCA if not October 1 and would that discrepancy between the LCA and the H-1B dates matter?
Only an immigration attorney can tell you the right course of action when faced with these issues. Although under certain circumstances, the USCIS has agreed to consider H-1 petitions submitted without certified LCAs, this is very risky because the USCIS will deny the H-1B petition if the LCA is finally denied. However, in these circumstances, the suggested practice is to enter the start date for the employment on the LCA as at least a month earlier to file the LCA a month before the H-1B and to give the DOL time to certify. The end date of the employment can be exactly three years from the LCA start date. So for example, the term of the employment for the LCA can be from September 1 to August 31 (3 years later), and the term on the I-129 can be from October 1 to August 31 of the third year (during the 3 year term).
Because of the popularity of the H-1B petitions, it is imperative that an efficient immigration attorney is on your side helping you with the applications and the hiring process, getting the petition ready and sending it as soon as the USCIS begins accepting applications. Historically, the 65,000 quota have been filled within the first week of April.