This is one of the sentences in Ch.1 of Wheelock.
It is from festino, festinare.
My question is, what tense/mood is “festina”, as it does not fit in with present, future or imprefect indicative active.
Or is it an irregular conjugation?
It’s Present Imperative Sing.
It’s the imperative. It’s used for giving orders. Wheelock is being cheeky by giving it to you so early. I don’t think you’re supposed to know it.
Keep in mind that any author of a language instruction book is required to throw in some words and grammar every now and then - prior to their proper introduction. It never fails.