I would recommend, if you can, to separate the SSID's completely so that you have a dedicated 5GHz only SSID, and a dedicated 2.4GHz only SSID (different name). This will makes things much smoother for your clients. Band-Steering works great on paper, but in reality its hit or miss, even with a great RF design.
You have to contact support to have them enable the option to create a 2.4GHz only SSID in your dashboard view, but once they do it will always show up as an option.