When This Happens 時

入る時 uses the dictionary form even though the sentence describes a habitual, repeated situation, “whenever you enter.” 時 doesn’t care whether the action already happened, is happening, or hasn’t happened yet, the form right before it just reflects that clause’s own internal timing.

い-adjectives attach directly, 寂しい時. な-adjectives and nouns insert な, 暇な時, 休みの時 uses の instead since 休み is a noun, the same pattern you’ve now seen across many grammar points, ので, のに, はず, ように.

時は, adding は, sets the whole time clause up as a topic, emphasizing a contrast or a general rule more strongly than 時 alone, “as for when I travel, [this is what I do].”