Very small period of time (6)
I believe the answer is:
minute
I believe this clue is a triple definition!
'very small' is the first definition.
(minute can mean tiny)
'period' is the second definition.
(minute is a kind of period)
'of' is a link.
'time' is the third definition.
(sixty seconds)
(Other definitions for minute that I've seen before include "Immeasurably small" , "Occupying very little space" , "60s" , "Little - bit of time" , "Infinitesimal" .)