There are 3 ways of querying return request list: by days, by minutes and by request itself. Which one should I use?

Basically, the feature of all the 3 APIs is the same. 

Only the query condition varies and you can develop as you need.

• By days : You can query up to 31 days. 
• By minutes : It is possible to query data of max 24 hours.  
• By request : You can check data based on cancellation(product) request number.