To right of Caliban expert conceals opening on stage (3,3)
I believe the answer is:
act one
'opening on stage' is the definition.
(I've seen this in another clue)
'to right of caliban expert conceals' is the wordplay.
'right of' suggests the final letters (letter on the rightmost end of the word).
'expert' becomes 'ace' (ace can informally mean very good).
'conceals' indicates putting letters inside.
The final letter of 'caliban' is 'n'.
'to'+'n'='ton'
'ton' put into 'ace' is 'ACT ONE'.
(Other definitions for act one that I've seen before include "First major segment of a play" , "Bit of drama" , "Dramatic beginning" .)