Is it legal to start working 10 days after the start date of the approval notice?

[questing]

I just received the email of the approval notice. The starting date on the approval notice is yesterday(09/29/15). The employer set up a start date 10 days later (10/12/15). Is the 10 days gap legal? I heard that one need to start working once upon the start date. Any information will be appreciated.