How to handle with much table connections in DB?

I want to make one Database with six tables,this six tables will have with each other some connection. So It's better I make various Foreign Keys for acess the information of the other tables or bound this tables through Inner Join ?

The name of the tables is : Minutes,hours,days,weeks,months,years.

And I want to do that : Minutes within the hour,hours within the day, day within the week, weeks within the month, month within years.