This time the metrical lines are unfavourable (7)
I believe the answer is:
adverse
'unfavourable' is the definition.
(similar in meaning)
'this time the metrical lines' is the wordplay.
'this time' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'the metrical lines' becomes 'verse' (I've seen this in another clue).
'ad'+'verse'='ADVERSE'
'are' is the link.
(Other definitions for adverse that I've seen before include "Hostile" , "Unfavourable to evaders" , "negative result" , "Opposed to or unfavourable" , "Inimical" .)