Set period at home filling legal document (10)
I believe the answer is:
Here is my best explanation:
'set' is the definition.
('determined' can be a synonym of 'set')
'period at home filling legal document' is the subsidiary indication.
'period' becomes 'term' (term is a kind of period**).
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'filling' means one lot of letters goes inside another.
'legal document' becomes 'deed' (deed is a kind of legal document).
'termin' inserted inside 'deed' is 'determined'.
(Other definitions for determined that I've seen before include "Resolved", "settled", "set", "Resolute", "With full strength and concentration", "Found out", "Firm", "Decided - resolute", "found" and "firm".)