どんな とき asks about a situation or an occasion in which the action in question is performed. In reply to this question, use an appropriate word before とき.
A: どんな 時、さんぽを しますか。
B: あたたかい 時、さんぽを します。
B: ひまな 時、さんぽを します。
B: やすみの 時、さんぽを します。
When asked a question which includes the question word いつ (when), answer with words which specify the time when the action takes place (e.g.,あさ[in the morning], にちようびに[on Sunday], 九時ごろ[at about 9 o'clock]).
The above words are modified by the preceding i-adjective, na-adjective, and noun in the same way that nouns are modified by them.