Since there is a limited number of H-1B visas every year, applications cannot just be submitted at any time during a year. The earliest date to submit an application is April 1 (six months prior to the beginning of the fiscal year), to start working October 1 at the earliest.
In practice, the result of the H-1B cap is that the USCIS stops the application process sometime between April 2 and April 5. Last year, for example, this happened 48 hours after the application process had begun, since at that point 150,000 applications had already been received over the past two days.
A random selection process will be used to pick out the forms to be reviewed. If a petition is selected during the random selection process, the employer will receive a written notice of approval or rejection. Therefore, it is not unlikely that H-1B petitions will not be reviewed even if the deadlines have been met. At the same time this means you have to hand in your H-1B petition exactly on April 1 in order to have a chance to have it reviewed and finally approved. For all petitions that are not randomly selected, however, the filing fees will be refunded. In addition, the petition will not be regarded as being rejected.
However, a new petition will not be possible before April 1 the following year (with work starting October 1), which leads to enormous waiting times. Quite frequently this means that the foreign worker will not be able to still get the position offered. Therefore, it is advisable to consider different types of work visa (E- or L-visa) in good time.