On a fine day, time for reading here in the garden? (7)
I believe the answer is:
sundial
'time for reading here in the garden?' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'on a fine day' is the wordplay.
'on' means one lot of letters go next to another.
'a fine' becomes 'dial' (I can't justify this - if you can you should give a lot more credence to this answer).
'day' becomes 'sun' (abbreviation for Sunday).
'dial' after 'sun' is 'SUNDIAL'.
Can you help me to learn more?
(Other definitions for sundial that I've seen before include "Solar timepiece" , "Shadow timer" , "It's an indication of the time" , "Primitive timepiece" , "Light clock" .)