You see compound adjectives done correctly a lot, so you probably get them correct yourself. You could say it’s a deep-seated habit. Here’s a guy who got it wrong:
Well, his mistake is justified. The rule is that two adjectives (or nouns used attributively) that modify a word together should be hyphenated. So we have the five-second rule about dropped food.
An adverb-adjective pair, though, usually isn’t hyphenated because the adverb modifies just the adjective. For example, we can have a very dark night, or a thoroughly spoiled custard. And “after holiday” is an adverb-adjective pair.
But sometimes that adverb-adjective pair just makes more sense as a compound adjective. “After” is an adverb, but he’s not saying that he’s doing something after the holiday; he’s saying that the bills are the after-holiday type. So here we have the uncommon case of an adverb-adjective compound.
It’s a judgement call, so think when you write.