Staff outside art gallery took turns (7)
I believe the answer is:
rotated
'took turns' is the definition.
(rotating is a kind of taking turns)
'staff outside art gallery' is the wordplay.
'staff' becomes 'rod' (both can mean a pole or stick).
'outside' means one lot of letters goes inside another.
'art gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'rod' placed around 'tate' is 'ROTATED'.
(Other definitions for rotated that I've seen before include "Turned in a circle around an axis" , "took part in revolution" , "Turner did?" , "Turned round" , "Spun" .)