Okay after some practice I was able to get it fairly consistently:

Thanks for the help!

Here's a video link to further explain:

In the video, "WAIT" appears above Cloud and Tifa's timebars before they can fill so I can't Cross-Slash with Cloud. It's really buggging me and I don't know what's wrong/what I can do. Maybe I'm leaking time in between using the Phoenix Down with Cloud and Big Guarding with Cid?

So I've been practicing the Jenova Life Aqualung backup strat on PS4 and I don't think the time bars are filling up properly. I know that you're supposed to Big Guard with Cid after using a Phoenix Down with Cloud to revive Tifa. The problem I'm having is Cloud and Tifa's ATB gauges don't fill before the Big Guard animation is done so I can't use Cross-Slash before Jenova gets a turn.

Is this a PS4-only problem? Do my characters have a lower Dexterity stat than their supposed to? Any help would be greatly appreciated.