And that "Sell If" is at the end of the month, right - not mid-month or with daily checks?
And then, before buying, confirm ^IXIC is above its 325 day SMA, right?

Mid-month, daily, or weekly, don't matter. Once a month at the regular trade date is good enough.
Most of the sell signals have a buy signal soon afterward, so you aren't gaining anything by selling early. It's just a small whiplash and doesn't have any big effect.

What *does* have a big effect is the times when timing takes you out for 9 or 18 or 38 months. And for those times, getting out a week or two earlier doesn't make any difference.

Timing is essentially a "see lightning, hear thunder" type of thing. (Indian joke, to pick braves qualified to go hunting pony soldiers. You don't have to be eagle-eyed and bat-eared, you just need to be able to tell there's something there.)

BTW, you can't have different periods for the sell signal and buy signal. Otherwise you could have one saying to BUY while the other says to SELL.