Medium out of time regards empty rows (5)
I believe the answer is:
tiers
'rows' is the definition.
(tier is a kind of row)
'medium out of time regards empty' is the wordplay.
'medium out of time' becomes 'tie' (I am not sure about this - if you are sure you should believe this answer much more).
'empty' says to hollow out the word (remove centre letters).
'regards' with its middle removed is 'rs'.
'tie'+'rs'='TIERS'
Can you help me to learn more?
(Other definitions for tiers that I've seen before include "Layers, levels" , "aprons for kids" , "I rest in layers" , "Rows; levels" , "Binders" .)