in a flash

Also, in a jiffy or second or trice. Quickly, immediately. For example, I'll be with you in a flash, or He said he'd be done in a jiffy, or I'll be off the phone in a second, or I felt a drop or two, and in a trice there was a downpour. The first idiom alludes to a flash of lightning and dates from about 1800. The word jiffy, meaning "a short time," is of uncertain origin and dates from the late 1700s (as does the idiom using it); a second, literally one-sixtieth of a minute, has been used vaguely to mean "a very short time" since the early 1800s; and trice originally meant "a single pull at something" and has been used figuratively since the 1500s.

The adverb has one meaning:

Meaning #1: without any delay
  Synonyms: instantaneously, outright, instantly