Basic info: If you are KO'd, in most cases you must roll to revive. To revive, you must roll 1d6 to get a result equal to or above a certain number, the revive roll (RR). RR starts at the character's recovery value (REC) and decreases by 1 every turn. On the turn when RR is 1, you are simply auto-revived since you would succeed the roll anyway. When you revive, you normally go back to full HP. The standard RV (thus the starting RR) is 5. Downtime is the amount of turns you need to take to revive, after being KO'd.

The expected downtime is what you should expect your downtime to be from getting KO'd if you average all your downtimes when playing with that REC. You won't actually be down for a fractional number of turns, but the number after the decimal tells you whether, say, you should expect to be closer to 2 or 3 turns, depending on whether your RV is 5 or 6.

Like everything else in the game, the exact KO downtime is up to chance. But minimum downtime is always 1 turn, unless someone plays Forced Revival before it's your turn (and then you revive with only 1 HP). Maximum downtime is always your REC, unless people play Forced Revival and then KO you again, in which case I think your revive roll resets.

The standard REC is 5. Some units have other RECs, Two units conditionally have REC of 1: Shifu Robot revives with only 1 HP and Sora (Military) revives with 2 HP. Additionally, the cards Extend and Hyper Mode (but only when user becomes KO'd while using it) effectively give REC 1 for the user's next downtime.

1 REC basically means they revive the next turn after they're KO'd.
0 REC basically means they revive immediately after being KO'd and don't lose a turn of actions for being KO'd.

As of the last update to this guide, the characters with each recovery value are as follows. So they start at these revive values. If you've failed a revive roll, then your next revive value (and thus expected downtime after that) is just one number lower.

6: Tomomo, Store Manager, Flying Castle, Sweet Breaker, NoName (ONLY when KO'd outside of battle), NoName (Head) (revives as NoName), Tomomo (Sweet Eater), Tequila
5: Kai, Poppo, Marc, Fernet, QP, Aru, Yuki, Suguri, Hime, Sora, Saki, Kyousuke, Krila, Kae, Kyoko, Alte, Sham, Sherry, Star Breaker, Nath, Kiriko, Miusaki, Ceoreparque, Yuki (Dangerous), QP (Dangeorus), Poppo (Mixed), Sora (Military) (ONLY when KO'd outside of battle), Aru (Scramble), Suguri (Ver.2), Tomomo (Casual), Tsih. Basically, most of the characters have 5 rec.
4: Peat, Syura, Nanako, Seagull, Robo Ball, Chicken
3: (none)
2: Tomato (revives as Mimyuu; see note below)
1: anyone who uses Extend and becomes KO'd, or uses Hyper Mode and becomes KO'd in the battle in which it was used. Also, without Extend or Hyper Mode, Shifu Robot (but it only revives with 1 HP), Sora (Military) (but ONLY when she is KO'd in battle, and when this happens, she only revives with 2 HP).
0: Mimyuu (revives as Tomato; see note below), NoName (ONLY when KO'd in battle)

Also, Magical Massacre (Tomomo's hyper) can decrease the REC value used for the next time a character is KO'd.

Note: Tomato and Mimyuu are a special case -- they officially have REC values of 3 and 1 respectively, but I've listed them here as 2 and 0 because unlike everyone else they can act on revive, meaning they spend one less turn KO'd. However, this changes some other game mechanics because some cards (e.g. Ubiquitous) cannot affect players that are KO'd while other cards can only hit players that are KO'd (e.g. Forced Revival) so it's not the same as having actual 2 and 0 REC. For example, if both Mimyuu and NoName are KO'd, during the time between turns that Mimyuu spends down at 0/3 HP as Mimyuu before reviving as Tomato, NoName would instead be at 2/2 HP as NoName (Head).

Trivia: the characters who appear in the chart at recovery values different from those shown on their character cards are:
* Tomato (due to acting on revive, and revives as Mimyuu)
* Shifu Robot (whose listed REC value is "-", but has the Auto-Repair ability)
* Sora (Military) (ONLY when KO'd in battle, and revives with 2 HP)
* Mimyuu (due to acting on revive, and revives as Tomato)
* NoName (ONLY when KO'd in battle)

The possibility-space of reviving looks like this: on any given roll, you either revive, or you fail and then the target value decreases by 1 and you repeat next turn. When the target value is 1, you automatically revive (because you could roll but any roll would be >= 1).

When we have a recovery value of 6, this means:
On the first turn you have a 1/6 chance of reviving.
On the second turn, you have a 2/6 chance of reviving...
...but this would only happen if you failed the first revive roll, which means there's a 5/6 chance of getting to the second turn at all.
On the third turn, you have a 3/6 chance of reviving...
...but this would only happen if you failed the second revive roll, which means there's a 4/6 chance of getting to the third turn after you've gotten to the second turn...
...but this, in turn, would only happen if you've failed the first revive roll, which means there's a 5/6 chance of getting to the second turn at all.

See how it follows a nesting pattern? We can make a chart of this:

If you multiply the probabilities together in each column, and sum up the columns, you get 1. That means you've covered all the possibiilties.

To get the expected value of turns that it'll take to get back up, multiply the probabilities together in each column, then multiply that column by the turn number, and then add up the columns.

For RV = 5, ignore the first row of fractions (that starts with 1/6), and start counting turns from 1 on your 2/6 chance roll.

For RV = 4, ignore the first two rows of fractions (starting with 1/6 and 2/6), and start counting turns from 1 on your 3/6 chance roll.

And so on.

If you do this right, this method should mean you're left with a simple "1" expected value when you have RV = 1. Which makes sense.

Anyway, that's how I got those numbers above.

(the digits after the underscore are the repeating digits; I don't know how to do an overline properly)