No, you are required to sign-on on the first day of unemployment. This ensures that your PRSI record is maintained.
Even if what your friend said was correct, you would still be without a JB payment for 5 weeks. Also, if you did wait 5 weeks to claim, you would have to account for what you did for the 5 weeks during which you did not claim which may cause more unnecessary hassle that you don't need at a time like this.
By delaying the claim you might also delay any entitlement to claim for a tax refund, or secondary benefits down the line should you need them e.g. a friend was made redundant at the beginning of May & is still waiting for their Medical Card application to be acknowledged, never mind to be issued.
It's best just to do things by the book.