After directional air dodging in Smash Ultimate, it seems like I'm sometimes able to act almost immediately afterwards while other times I can fall all the way to the blast zone without being able to jump afterwards. Is the lag always constant after air dodging and I'm just crazy, or is the lag determined by something (percent, or maybe it stales the same way rolling on stage does?)?
As of Update 3.0.0...
Changes have been made to the amount of lag on dodges. From the change notes:
Made it easier to be penalized for continuous dodging.
In the initial testing, it looks like this means that intangibility frames are even shorter and FAF is even later for all levels of staleness on dodges, so the numbers below may no longer be entirely accurate.
However, I'll leave the answer as it was below for historical purposes.
Smash Ultimate is different from all other titles in the series in that dodges now stale like other moves (I've heard this called both "dodge staling" and "dodge decay").
This means that the more you dodge, the slower the dodge will come out, and the more lag you'll have after dodging. This staling mechanic encompasses every dodge. This means that more rolls and spot dodges on stage will stale your air dodges off-stage.
For example, here's Wolf's back roll frame data (taken from here):
Fresh: Int: 5-16 FAF: 34
1 Stale: Int: 5-14 FAF: 38
2 Stale: Int: 6-14 FAF: 41
3 Stale: Int: 7-14 FAF: 45
4 Stale: Int: 8-14 FAF: 48
5 Stale: Int: 9-14 FAF: 51
As you can see, the Intangibility of the back roll starts later, ends earlier and most importantly the First Actionable Frame (first frame you can act) gets waaaaay later.
The same is true for air dodges. The more you've been dodging (whether in the air or on the ground), the longer it'll take for you to be able to act out of an air dodge. Directional air dodges specifically can be brutally punishing if they're exceedingly stale.
But here's where things get interesting. The FAF on air dodges actually depends on the direction you air dodge in!
Using Fox as an example, his un-stale FAF values look like:
Fox Up: 76
Fox Diagonal Up: 70ish
Fox Side: 65
Fox Diagonal Down: 60ish
Fox Down: 54
If you're thinking to yourself that these numbers look pretty rough, you're right on the money. 60 frames is one full second! And if the rolls are anything to go by, these FAF values can be up to 20 frames greater at max stale. So a max staled upwards air dodge might leave you in free fall for more than 1.5 seconds!!
That being said, the air dodge with the best FAF of them all is neutral air dodge. Fox's FAF for neutral air dodge is only 38! That's a whopping half of an upwards air dodge!!
So if you find yourself dying to off-stage air dodges often, I'd strongly suggest working on doing neutral air dodges instead of trying for a directional air dodge as you'll be far less likely to fall too low and kill yourself before you can act.
The Beefy Smash Dudes just put out a video on the new air dodges a few days ago. In it they say most of what I've said above in terms of numbers. However, they claim that a staled air dodge won't actually have an increased FAF, it'll just have less Intangibility frames.
In addition, they also show that the FAF for directional air dodges is dependent on fall distance (or more accurately the frame data is set to make it look like fall distance). This means that fast fallers like Fox will actually have some of the lowest frame counts for their FAF after a directional air dodge (so maybe I should've used someone else up there to show how slow they are) while someone like Jigglypuff will be stuck falling for a longer time (though she'll fall the same distance as Fox before being able to act).