Dawn to stand up and boast (8)
I believe the answer is:
cockcrow
'dawn' is the definition.
(I know that dawn can be written as cockcrow)
'stand up and boast' is the wordplay.
'stand up' becomes 'cock' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other).
'boast' becomes 'crow' (to crow about something is to boast about it).
'cock'+'crow'='COCKCROW'
'to' is the link.
Can you help me to learn more?
(Other definitions for cockcrow that I've seen before include "First light of day" , "early morning" , "Daybreak" , "Sunrise" , "Dawn as signalled by rooster" .)