I've attached an alternate method, instead of moving a value into N7:1, I use a self resetting timer done bit and flip flop logic to toggle a bit every 60 seconds. Then used bit true and false conditions to alternate "main" and "standby" solenoids.
Didn't give it a whole lot of thought, but I believe it will work, let me know if you try it.
Ken
edit: This program was written using ver 6.0, I can save differently if needed.