At sea patrol boat loses a little time in Welsh seaside town (4,6)
I believe the answer is:
port talbot
'welsh seaside town' is the definition.
'at sea patrol boat loses a little time' is the wordplay.
'at sea' is an anagram indicator.
'loses' indicates named letters should be taken away.
'little time' becomes 't' (abbreviation for time).
'patrol'+'boat'='patrolboat'
'patrolboat' with 'a' removed is 'ptrolboat'.
'ptrolboat' is an anagram of 'porttalbo'.
'porttalbo'+'t'='PORT TALBOT'
'in' is the link.
(Other definitions for port talbot that I've seen before include "Welsh industrial town" , "South Wales town" , "Welsh steel town" , "Port, town in S. Wales" .)