At sea patrol boat loses a little time in Welsh seaside town (4,6)
I believe the answer is:
Here is my best explanation:
'welsh seaside town' is the definition.
'at sea patrol boat loses a little time' is the subsidiary indication.
'at sea' indicates an anagram.
'loses' indicates named letters should be taken away.
'little time' becomes 't'.
'patrolboat' with 'a' taken away is 'ptrolboat'.
'ptrolboat' anagrammed gives 'porttalbo'.
'in' is the link.
(Other definitions for port talbot that I've seen before include "Town in South Wales", "Port, town in S. Wales", "Welsh steel town", "South Wales town" and "Welsh industrial town".)