discounted hours; reduced rate hours
Refers to time periods when a discount or reduced rate applies, such as off-peak hours for electricity, phone calls, or services.
With this plan, it's cheaper to make calls during discounted hours.
The discounted hours for electricity rates are at night.
割引 means 'discount' in general, while 割引時間 specifically refers to the time period when the discount is applied.
Compound of 割引 (わりびき, 'discount') and 時間 (じかん, 'time, hours').