Henry to appear in a short time – and again and again? (6)
I believe the answer is:
thrice
'again and again?' is the definition.
(I've seen this in another clue)
'henry to appear in a short time' is the wordplay.
'henry' becomes 'H' (symbol for the unit of electrical inductance).
'to appear in' indicates putting letters inside.
'a short time' becomes 'trice' (a short time, eg in phrases like 'in a trice').
'h' put inside 'trice' is 'THRICE'.
'and' is the link.
(Other definitions for thrice that I've seen before include "Archaic word for three times" , "On three occasions" , "Once, once more and yet once more" , "In threefold degree" , "Several times" .)