Ruby on rails convention for naming date/time fields

I want to make a scaffold like this:

rails generate scaffold Job started_at:datetime completed_at:datetime price:decimal paid_at:datetime estimated_completion_at:datetime comment:text

I've added "_at" to the datetime fields because that seemed to be the convention as rails timestamp fields are either "_at" for datetime or "_on" for date. But is this actually a convention? Is it OK if I just have "paid" instead of "paid_at" and "completed" instead of "completed_at"?

I really want to get this right from the start. I've been programming in c# for years but I'm new to ruby on rails. I like all the conventions and I want to make sure I'm doing this the proper 'rails way'.