The most common and most likely answer to this crossword clue is the 10 letter word SEASONALLY
I've seen this crossword clue in The Daily Telegraph
S
E
A
S
O
N
A
L
L
Y
More clues leading to the result SEASONALLY
Buddy explains!

The straight part
We know that "at certain times" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case at certain times = seasonally.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SEASONALLY mean?
SEASONALLY adverb- Occurring every season.
- Occurring only in season.