Could I use a restaurant voucher during happy hour?

Hi. I have a voucher for a restaurant I want to go to. It’s about $20 but the terms say “cannot be combined with any other discounts or offers.”

Does anyone in the restaurant world know if that applies to Happy Hour? Technically it’s a discount on food and drinks. I don’t know what the technicalities are and would like to get the most bang for my buck since $20 is only enough for a normal price appetizer and a fountain drink