That minuscule fraction of time it takes your brain to realize that you've just made a GIGANTIC mistake and reconcile the fact that it is too late.

Got the covid-19 vaccine

That minuscule fraction of time in which you realize that you've just made a BIG mistake.

The momentary panic that occurs when something irreversible goes wrong. Can also be used to describe something that turns out to be reversible although you were worried at the time it wasn't.

The split second between hitting the "send" button on the computer to send an email, and realizing that there is a serious problem with the email (such as using "reply all" instead of reply to sender, especially for an inflammatory email, or seeing a nasty grammatical mistake after the send button has been hit.

The exact moment where you realize what a big mistake you have made.

Ohno-second is the period of time that is spent waiting for the debit or credit card you just submitted for payment to respond - hopefully with the word "approved", and hopefully not "payment declined" (Oh No!) The ohno seconds are usually spent mentally reviewing your account balances and recent purchases or date of your automatic deposit. MUCH longer than a nano-second, this word is most appropriate while being at the front of a long line in a store with people looking over your shoulder and the pimple-faced clerk glaring at you as if to say "I know YOU can't afford this purchase, loser".