Last-minute or last minute? Is Hyphen needd in the middle or not?

Ann the rule is, when two or more words come modifying a third, they are joined by a '-', giving us the 'compound modifier'. Technically I guess it oughta be 'last-minute'

In the case of a third mem, as 'almost last-minute decision,' the first isn't used, which I often deplore 'cause its omission can affect meaning, as in 'third criminal-party involvement' usually intended as a single involvement of a kind w/ three bad guys

...whereas, technically, w/o the '-', means three acts by a bad guy