Silly tall tales should all be ignored - they're the most behind schedule (6)
I believe the answer is:
latest
'silly' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'tall tales should all be ignored they're the most behind schedule' is the wordplay.
I cannot quite see how this works, but
an anagram of 'tales' is 'lates' which is within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for latest that I've seen before include "Most recent or most unpunctual" , "style of today" , "Most recent, hot off the press" , "Most recent (news)" , "Up-to-the-minute" .)