Permit takes time for Latvian (4)
I believe the answer is:
Here is my best explanation:
'latvian' is the definition.
'permit takes time' is the subsidiary indication.
'permit' becomes 'let' ('let' can be a synonym of 'permit').
'takes' means one lot of letters go next to another.
'time' becomes 't'.
'for' is the link.
(Other definitions for lett that I've seen before include "Balt", "Native of Latvia", "Baltic citizen", "northerner", "native" and "East European".)