White Christmas may ultimately embody present time (5)
I believe the answer is:
snowy
'white' is the definition.
('snowy' can be similar in meaning to 'white')
'embody present time' is the wordplay.
'embody' indicates putting letters inside (embody can mean include or incorporate).
'present' becomes 'now' (I've seen this before).
'time' becomes 'sy' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'now' inserted within 'sy' is 'SNOWY'.
'christmas may ultimately' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
(Other definitions for snowy that I've seen before include "Wintry" , "Tintin's dog - describing winter weather" , "Covered in flakes" , "- Mountains; - owl" , "Tintin's (white?) dog" .)