点 (diǎn) has two common uses at this level: as a noun for 'dot, point, or o'clock' (几点了? 'what time?'), and as a classifier for small amounts (一点水 'a little water'). For telling time, use 点 for the hour number (1点 1 o'clock); 时 (shí) appears in fixed words like 小时 (hour) or 时候 (time), not for simple hour telling. For a small spot or speck, 点 is more general; 点子 (diǎn zi) is a separate noun that specifically means a dot or an idea.