Can H1B COS choose a later start date than Oct 1?

[revat6]

I was selected in the second lottery and because of personal circumstances, I can only pursue a change of status. My company's attorney told me that if I commit to COS, we can still choose a later router login 192.168.l.l.link/ start date than OCT 1 to utilize more of my OPT period. I haven't found anything online to confirm this statement but I'm unable to get ahold of my company's attorney. Can anyone help explain this to me? Many thanks!