At that time, one hotel in ten (4)
I believe the answer is:
then
'at that time' is the definition.
(at some former time)
'one hotel in ten' is the wordplay.
'one hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'h' inserted into 'ten' is 'THEN'.
(Other definitions for then that I've seen before include "At that time; next" , "Consequently" , "Subsequently - previously" , "soon?" , "Afterwards - as a result" .)