Change your background at a specific time (Mac OS X). Use `crontab -e` to edit your crontab:

crontab

0       10      *       *       *       osascript ~/bin/Flow.scpt
0       12      *       *       *       osascript ~/bin/No\ Flow.scpt
30      14      *       *       *       osascript ~/bin/Flow.scpt
30      16      *       *       *       osascript ~/bin/No\ Flow.scpt

Flow.scpt

tell application "Finder"
	
	-- wrapped in a try block for error suppression
	try
		
		set mainDisplayPicture to "/Users/claytonwatts/Pictures/Flow.jpg"
		
		-- set the picture for additional monitors, if applicable
		tell application "System Events"
			
			-- get a reference to all desktops
			set theDesktops to a reference to every desktop
			
			-- handle additional desktops
			if ((count theDesktops) > 1) then
				
				-- loop through all desktops (beginning with the second desktop)
				repeat with x from 1 to (count theDesktops)
					
					-- apply image to desktop
					set picture of item x of the theDesktops to mainDisplayPicture
					
				end repeat
				
			end if
			
		end tell
		
	end try
	
end tell

No Flow.scpt

tell application "Finder"
	
	-- wrapped in a try block for error suppression
	try
		
		set mainDisplayPicture to "/Users/claytonwatts/Pictures/No Flow.jpg"
		
		-- set the picture for additional monitors, if applicable
		tell application "System Events"
			
			-- get a reference to all desktops
			set theDesktops to a reference to every desktop
			
			-- handle additional desktops
			if ((count theDesktops) > 1) then
				
				-- loop through all desktops (beginning with the second desktop)
				repeat with x from 1 to (count theDesktops)
					
					-- apply image to desktop
					set picture of item x of the theDesktops to mainDisplayPicture
					
				end repeat
				
			end if
			
		end tell
		
	end try
	
end tell