Pre-Christmas period restricts Queen broadcast times, becoming commercial (13)
I believe the answer is:
advertisement
'commercial' is the definition.
(thesaurus)
'pre-christmas period restricts queen broadcast times' is the wordplay.
'pre-christmas period' becomes 'advent' (I've seen this before).
'restricts' indicates putting letters inside.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'broadcast' indicates anagramming the letters.
'times' with letters rearranged gives 'tisem'.
'er'+'tisem'='ertisem'
'advent' placed around 'ertisem' is 'ADVERTISEMENT'.
'becoming' is the link.
(Other definitions for advertisement that I've seen before include "Public promotion" , "Placard" , "Commercial promotion" , "plug" , "trailer" .)