"on time" vs. "on-time"

I'm in the "on-time" camp when it comes to describing, for example, delivering something by the deadline. Is this the correct usage?

In a situation where you're using the phrase on time as an adjective (basically a synonym of punctual) preceding the noun, then it's fairly common to use a hyphen. Examples I was able to quickly pull up were things like

On-time delivery is our goal.

On-time flight departures were up 10%.

On-time performance is an important ingredient

However, if you're using the phrase on time as an adverb to describe when the verb is going to happen, the hyphen is not appropriate. For example:

We will deliver your package on time.

Your flight will depart on time.

Finally, if you're using on time as a predicate adjective, I would not use the hyphen.

Your delivery was on time.

When a multiword phrase is used as an adjective, then you use hyphens to join up the words. Otherwise you don’t.

We provide on-time delivery.

Hyphen because on-time is used as an adjective modifying delivery

We will deliver it on time.

No hyphen because it is used as an ordinary idiomatic prepositional phrase.

Adverbial phrase: on time

This describes the punctual manner in which an action is undertaken. Examples:

• My package was delivered on time.

• Did he arrive on time?

• Am I on time?

Adjective: on-time?

My guess is that this usage is informal. Certainly it is possible to hyphenate words to convert them into adjectives. A good example is the noun cutting edge, which can be used as an adjective thus:

• MIT is a hot spot for cutting-edge physics.

on time is special, as it is an adverb, but it is not uncommon to see it as an adjective thus:

• We give you on-time solutions to your problems.

I find that this sort of usage occurs mostly in marketing, especially in the delivery business. As a personal matter of taste, I would substitute on-time with other established adjectives in formal writing. Examine the following sentences:

•  We offer on-time deliveries.

•  We offer prompt deliveries.

•  Our deliveries are on time.

I would prefer the second to the first for formality's sake. The third sentence, however, is perfectly fine and acceptable in all situations. It is important to recognize where on time is used as an adverb, in order to avoid incorrect hyphenation. This is a mistake I imagine is commonly made.