How to JUST store hours and minutes in db?

I would use a decimal field so 8:00 AM (0800) would be 8.0 and 4:30 PM
(1630) would be 16.5.

AFAIK, there is no plugin to do this, but it shouldn't be a difficult
coding process.

Ryan is correct.

In your migration

  create_table "products" do |t|
    t.column "opening_time", :time
    t.column "closing_time", :time

--or in Rails 2--

  create_table "products" do |t|
    t.time "opening_time", "closing_time"