During my time learning Chinese, I've heard two distinct word orders when referencing the time at which something will occur. For example, I was taught to say 今天我想吃早饭 to talk about 今天, 明天, etc, but I was taught to say 我想八点钟吃早饭 when speaking about a specific time, which seems a rather different word order.

What are the rules surrounding the word order when talking about time in this context? Are both ways acceptable (that is, would 八点钟我想吃早饭 and 我想今天吃早饭 also be okay)?