Leaders in Puerto Rico getting on almost too quickly (6)
I believe the answer is:
pronto
'quickly' is the definition.
(I've seen this before)
'leaders in puerto rico getting on almost too' is the wordplay.
'leaders in' says to take the initial letters.
'getting' means one lot of letters go next to another.
'almost' means to remove the last letter (most of the word but not all of it).
The first letters of 'puerto rico' is 'pr'.
'too' with its last letter taken off is 'to'.
'pr'+'on'+'to'='PRONTO'
(Other definitions for pronto that I've seen before include "Right away, quickly" , "Quickly, without delay" , "Right now, immediately" , "Quickly, immediately" , "Right now, amigo" .)