I would really appreciate seeing any macros you will share....
This is I stripped down version of my macros. I do a few other things in mine that you don't need to do for the basic flashing.
Ok this arrangement uses 3 macros, 1 dummy appliance module, and 1 flag.
For my example, I've used macros "P4 ON", "P5 ON", "P5 OFF", "Dummy module defined as P4", and flag 2
Flash Lights - Loop P4 On and Flag Status On exactly 2
House Code C All Lights On
Delay for 5 Seconds ;Pick your own delay times
House Code C All Units Off
Delay for 5 Seconds ;Pick your own delay times
P4 ON
Flash Lights - Start P5 On
Set Flags [2] Flag Command
P4 ON
Flash Lights - Stop P5 Off
Clear Flags [2] Flag Command
Delay for 2 Seconds
Clear Flags [2] Flag Command ;Redundant command ideally not needed but this is X10 you know.
Delay for 15 Seconds
House Code C All Units Off ;Insures that lights are left off. If you prefer you can send an "All Lights On" or omit all together.