时候

时候 is a frame word, and it always leans on whatever comes before it. So you say 在吃饭的时候, 在下雨的时候, or 今天白天的时候. As seen in 《很贵的苹果》, when saying 今天白天的时候，我去我家这边的超市买东西, the 的时候 hangs off 今天白天 — the moment you are pointing at. Strip that piece away and 在时候 floats with nothing to hold on to. Native ears hear it the way you hear 'at time' in English, which is to say, as a mistake.

English squeezes both ideas into the single word 'time', and Chinese splits them apart. 时候 is a moment tied to something happening — 我回家的时候, 吃饭的时候, 小的时候. 时间 is measurable clock or calendar time you can have, kill, or run out of — 你有时间吗? That is exactly why 什么时候 asks 'when?', while 你有时候吗 sounds like gibberish. If you want to ask 'how long', reach for 多长时间 instead.

Chinese question words do not jump to the front of the sentence the way English ones do. 什么时候 stays right in the slot where the answer would land: 我明天去 becomes 你什么时候去? Subject first, then 什么时候, then the verb. Opening with 什么时候 sounds like you translated 'When do you...' word by word from English. The same rule covers 谁, 什么, and 在哪儿, so this one habit pays off everywhere.

的时候 simply glues onto whatever sits in front of it, and 小时候 turned into a fixed chunk because people say it constantly. 我小的时候 is a touch more explicit, 小时候 is shorter and more casual, and both sound fine at the dinner table. What breaks is 我是小的时候, which sounds like you are defining yourself as 'a little time'. Keep 是 out of a 的时候 phrase unless you genuinely mean 'is'.