Define "long enough". On the profile I posted I get a ceiling after 7-ish minutes at 90-ish fsw, that would be the "long enough" by your definition. By PADI RDP definition, it's 21 minutes before the "optional means mandatory" grey boxes, and 25 to NDL=0. That's ~300% difference.
Long enough: The time it takes to run your NDL to zero based on the dive computer that you have chosen, the algorithm it uses, the conservatism or GF modifications that you use, the profile that you are actually running, and the mix that you tell your computer that you are breathing.
The fact that LE is a different number if you use different variables is irrelevant. Why would you imply to a recreational diver that the NDL that his or her dive computer generates during a dive is somehow up for negotiation or analysis? Being "in deco" isn't some absolute quality that you can measure in a diver, the phrase only has meaning in the context of all of those variables.
And just to silt things up more for the recreational divers reading this, there are a whole bunch of other variables that the computer can't account for that can get you bent! You can get bent by staying within NDLs, and you can blow off deco and have no symptoms of DCS. It's simply not possible to model physiology that accurately, but your standard recreational dive computer will do a good job of making the risk of DCS acceptably low.
Here, 90 FSW for 20 minutes on air. Same dive repeated on two successive days.
Day 1, GF 30/70 -> 8 minutes of deco
Day 2, GF 99/99 -> NDL dive
So was I "in deco" on day 1? On day 2? Both? Neither?
What this means is that a diver is "in deco" if their computer tells them that they have gone past NDL=0, or if it generates a mandatory stop, or if it generates a ceiling. Even if it clears on ascent, or if the stop goes away. And if that diver has no technical training, they should avoid that condition by
not staying underwater so long, based on their own chosen means of tracking N2 loading (i.e. their DC).
Does RDP's "optional safety stop required" mean it's a mandatory stop?
Just trying to get the terminology right so that further discussion will be clearer. And I appreciate your replies.
This kind of fuzzy language is not helpful, not sure what it means for something to be both optional and required. Maybe I need some context for that language, don't have an RDP.