The most common and most likely answer to this crossword clue is the 2 plus 3 plus 7 letter word UP AND RUNNING
I've seen this crossword clue in Financial Times
U
P
A
N
D
R
U
N
N
I
N
G
More clues leading to the result UP AND RUNNING
Buddy explains!

The straight part
We know that "Fully functional/like a jogger before dawn" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fully functional/like a jogger before dawn = up and running.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.