Behind schedule, but initially in high spirits (7)
I believe the answer is:
belated
'behind' is the definition.
(I've seen this in another clue)
'but initially in high spirits' is the wordplay.
'initially' suggests taking the first letters.
'in high spirits' becomes 'elated' (similar in meaning).
The first letter of 'but' is 'b'.
'b'+'elated'='BELATED'
'schedule' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for belated that I've seen before include "delayed" , "Out of date" , "Tardy" , "After the proper time" , "Bleated, being too late" .)