Hi Adam,
Try this 'Insert time' Automator Service (Dropbox dowload) which includes the script below.
To install doubleclick the .workflow package. You may have to click 'Open anyway' in System Preferences > Security & Privacy. It will then appear automatically in your Numbers > Services Menu.
Then you can assign a keyboard shortcut here (System Preferences > Keyboard):
Thereafter, whenever you need to insert a time just click a cell in Numbers and hit the keyboard shortcut you assigned. Very similar to Excel.
If you ever want to remove the service just hold down the option key in Finder and Go > Library > Services.
SG
--inserts time in 24-hr format
set the clipboard to (do shell script "date +%H:%M")
tell application "Numbers"
activate
tell application "System Events"
keystroke "v" using {shift down, option down, command down}
end tell
end tell
--end of script