Think I'm home in time (7)
I believe the answer is:
Here is my best explanation:
'think' is the definition.
('imagine' can be a synonym of 'think')
'i'm home in time' is the subsidiary indication.
'home' becomes 'in' ('he's home' can mean 'he's in').
'in' means one lot of letters goes inside another.
'time' becomes 'age' (age is a kind of time).
'in' inserted within 'age' is 'agine'.
(Other definitions for imagine that I've seen before include "Suppose; conceive", "Form a mental image in the mind", "Conceive in the mind", "See something that doesn't exist", "John Lennon classic (just think of it!)", "Mentally picture", "Conjure up in mind,fancy", "Visualise", "Conceive; fancy" and "Lennon song - dream".)