The proper date is at the beginning of September (6)
I believe the answer is:
sedate
'the proper' is the definition.
(I've seen this in another clue)
'date is at the beginning of september' is the wordplay.
'is at' says to put letters next to each other (I've seen this in other clues).
'the beginning of september' becomes 'se' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'date' put after 'se' is 'SEDATE'.
Can you help me to learn more?
(Other definitions for sedate that I've seen before include "Dignified - staid" , "Calm and dignified in manner" , "Dignified and subdued" , "Slow" , "Staid and sober" .)