I personally wouldn't plan anything like that if I was doing a recreational dive in a quarry.
I'd check I had some gas and I'd jump in. I'd keep an eye on my computer to make sure I didn't get more than a few minutes of required decompression stops.
I'd turn the dive when I got bored/cold or when I felt the gas was getting a bit low.
Not this. No offense, but if this was meant seriously, it is idiotic advice for a pair of new divers seeking guidance on how to conduct their first dives without supervision. If it was a joke, sorry if I didn't get it.
Gas planning is only a part - an important part, but only a part - of planning your dive.
Vis a vis the video above, it would be a huge disservice to the OP to have this thread go off on some tangent about UTD's Min Deco philosophy. I'll simply say that you can read all about it on other threads and that it is not without (a ton of) controversy. It should not be controversial to suggest out that unless/until you get some training on it, and make an informed decision as to whether it is a sensible thing, you would be wise to stick with what you learned in training about calculating NDLs and ascent strategy, which was likely to observe the NDL limits on your computer/tables and end the dive by ascending at 33'/min with a 3-5 minute safety stop at 15-20'.
The larger point of the video, and perhaps the reason it was posted was a good one, however. Be a thoughtful diver. The "rock bottom" concept of having enough gas to get you and a buddy to the surface - safely - rather than some arbitrary number is a good one. But, you don't have to adopt the whole "min deco" thing in order to do some math and figure out a realistic & prudent turn pressure.
That's just one part of dive planning/leading. Mostly, it is about the mind-meld so that you and your buddy have a common objective, expectations, comfort, etc., and addressing some potential contingencies.
A few random thoughts to think/talk through:
What's the plan if there's a problem? Where are you leaving the car keys and cell phone? Are there other people around to help if there is an emergency?
What's the goal of the dive? Are we checking out the sunk car, practicing skills, etc? Have some sort of general expectation at least -- " we're going to surface swim to the buoy, descend on the platform, then head left and look for the xzy" or whatever. What's "Plan B" if we can't find the car, or whatever? It's far easier to figure this out on the the surface than to descend, look at each other and start shrugging shoulders.
Are there any particular hazards? Current, overhead environments, etc?
If needed, establish ground rules ("I'm not comfortable penetrating that wreck" or "I'd like to limit the dive to XZY time")
What is our plan if we get separated? Discuss this every time.
Who is leading? Maybe take turns. Both of you are equally responsible for maintaining awareness, keeping track of location, being aware of NDLs and gas supply, etc.
Equipment/buddy check before entry. Valves on? Regs and BCD inflator working? Gas supply sufficient? Bubble check? Nothing loose or dangling?
Pay attention to whatever navigational "assets" you have to get you back to where you started without a long surface swim.
Observe each other and periodically make eye contact and/or do an "okay" check. Watching your buddy from behind may not tell you if they are stressed, scared, or otherwise uncomfortable. Making periodic eye contact and affirmatively asking will give you a lot more information. This can become less frequent later, but for now when you are probably both a little nervous, it is a good thing.
Also ask periodically what their tank pressure is. It is useful information to you (because their gas consumption may be the limiting factor) and it is a polite way of ensuring that they are monitoring their gauge.
Remember either of you can end the dive at any time. No questions asked, ever. Make sure you empower your buddy on this. Expressly tell each other that it's fine to thumb the dive and no one should feel any pressure to continue if they are uncomfortable. Your GF will be more comfortable on the dive knowing she has the power to end it if she becomes uneasy.
Bring a slate or wetnotes. Especially early in the process when your hand signals may not provide enough underwater vocabulary.
If you are planning on practicing skills, discuss that in advance. Your GF will not appreciate it if you initiate an air sharing drill without having warned it her it might be happening (although eventually having standing permission to simulate OOA on local dives can be good practice).
After the dive, talk about what went well and what didn't -- with the plan, with communication, gear, whatever. Talk about it and fix it.
It won't take long to feel much more comfortable, just start with simple dives. A lot of divers forget how intimidating it can be the first time you do it on your own. Have fun with it and in no time much of this will become automatic.
