Newspaper and music magazine once featuring old timer (9)
I believe the answer is:
metronome
'timer' is the definition.
(device keeping musical time)
'newspaper and music magazine once featuring old' is the wordplay.
'newspaper' becomes 'Metro' (London newspaper).
'and' says to put letters next to each other.
'music magazine once' becomes 'NME' (UK music magazine no longer available in print).
'featuring' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'nme' going around 'o' is 'nome'.
'metro'+'nome'='METRONOME'
(Other definitions for metronome that I've seen before include "Pendulum to indicate tempo of music" , "Device for keeping time" , "Instrument for beating time in music" , "Device to help regulate tempo" , "Device to indicate tempo" .)