Waves to friend at certain times (10)

'waves to friend at certain times' is the definition.
I can't tell whether this definition defines the answer.

'waves to friend at certain times' is the wordplay.
'waves' becomes 'seas' (I've seen this in another clue).
'to friend' becomes 'ally' (an ally is a friend or supporter).
'at' means one lot of letters go next to another (I've seen this in other clues).
'certain times' becomes 'on' (I can't justify this - if you can you should believe this answer much more).
'ally' after 'on' is 'onally'.
'seas'+'onally'='SEASONALLY'

Can you help me to learn more?