As PP said, midnight eastern.
FYI, several people from our sailing have reported issues with booking Palo brunch in that it only allows you to select one person from your party (if you have a party of two, for example). This was the case for me. Many of them have then called
DCL and found out that this DOES reserve for both people in the room. I'm just letting you know so that if this is happening to you, you know it is okay.
Good luck!