To avoid any possibility of disappointment, my advice is to always make PS as soon as you know where and when you want to eat. Lots of folks report never having any problems just walking in--but I go in September quite often, and at some of the more popular places (especially on weekends) I've seen parties as large as yours--without PS-- turned away. Places such as Flying Fish, California Grill, Yachtsman Steakhouse. Just 2 trips ago, we ate at Flying Fish and saw a party of 8 and another party of 12 turned away on a Saturday night. They wouldn't even let them sit at the bar--no seats there either!! When they asked where they might eat on the Boardwalk, the hostess suggested they try the ESPN club!!
If you do decide to "wing it" at least try to eat very early in the evening--that seems to be the least crowded time at restaurants such as those I mentioned.