See clip from Attorney Rajiv S. Khanna's conference call video that addresses this question.
Well you don’t have any time to lose. Apply right away. The way it works is your H-1 application must reach the USCIS on April 1st no earlier and usually no later. Sometimes they give us three to four days but normally April 1st is the day the quota opens and that’s pretty much the quota closes as well and there are usually more applications received by the government than they have visas almost two to one ratio maybe more sometimes and then there is a lottery held and if you get selected in the lottery then your H-1B gets approved. You go for a visa stamping and you can enter USA no earlier than 10 days before October 1st when your H-1B visa period starts.
What is this thing about October 1st?
The US government fiscal year begins on October 1st so all the quotas including green card and H-1’s they get reset on October 1st. H-1 you can apply six months ahead of the start date which is April 1st so that’s why you file on April 1st and you begin working on October 1st but you can enter USA ten days ahead of October 1st.