I'm used to on Windows of using the keyboard to choose a popup combo box menu item in a window and then once it is selected, using the tab key to move to the next field for entry.
I'm finding this does not work for Chrome on Macintosh OS X Lion.
What is the keyboard key to use in this case?
Here is an example, 05/08/12 is selected using keyboard, now want to tab to Next button with a single keystroke and choose the current item of 05/08/12 (presently must first hit space, and then hit tab, two keystrokes):

spaceorreturn, thentabthrough the form elements until you're at the Next button. But maybe I'm not understanding you correctly — is your real question whether you cantabright away without selecting the date? – slhck♦ May 5 '12 at 19:41