New and Lied To Already

After a disasterous break from a previous employer I found a new position with considerably more money, and accepted though I have not officially begun yet. Through some initial knowledge transfer I found out my new boss lied about one of the benefits options that apparantly everyone gets, but was not offered to me because he stated no-one gets it.

The question: how do I confront my new boss? Should I hold on to this info until my end of month report, and bring it up, or confront as soon as possible? Leaving is not an option due to financial and other implications I cannot state here.