Language & Grammar discussion

I have a question - what is the correct spelling of minute to use when writing about a period of time e.g. the class had a 45 minute discussion or the class had a 45 minutes discussion? Always wondered what the correct spelling should be (singular or plural) as it has been written both ways, most often in the singular but if it is more than one minute should it be plural?

Many thanks for your help.

It should be singular. The noun is "discussion" so "45-minute" (and it should have a hyphen) is now not individual minutes, but one adjectival term modifying "discussion."

Ruth wrote: "It should be singular. The subject of the sentence is "discussion" so "45-minute" (and it should have a hyphen) is now not individual minutes, but one adjectival term modifying "discussion.""Brilliant!! - thanks Ruth