What are the rules surrounding word order when talking about time (e.g. are 八点钟我想吃早饭 or 我想今天吃早饭 okay)?
I think it's just the same when it is in english:  

今天我想吃早饭 - Today I want to have breakfast  
我想八点钟吃早饭 - I want to have breakfast at eight  

我想今天吃早饭 - I want to have breakfast today  
八点钟我想吃早饭 - At eight, I want to have breakfast 


All these sentence make sense and are acceptable.