Is 24×7 support a requirement?
Maybe.
The success of all support offerings comes back to your customers: what do they need? what do they want? You may have a customer base that simply requires 24×7 support so that it should be included in all support offerings. For instance, if you work under a SaaS model, or your products are typically used in mission-critical environments, you must provide 24×7 support simply to be credible.
Other environments are more flexible and allow shorter support hours. Say you sell appointment software for dentists’ offices. Since few are open at night, a business-day offering may be fine. (In this situation, however, offering extended-hours support or Saturday support may make sense.)
Some enterprise products may not require 24×7 support. Say you sell software for CAD that’s typically used during the day and is considered mission-critical. The majority of your customers would not require nighttime or weekend support so you can offer at least some packages for business-hours support only.