The adverbial clause

A comma is required before or after an adverbial clause, depending on whether it begins or ends a sentence, if it functions as a nonrestrictive clause, Example:

When Anthony woke up a few seconds later it was to the most [godawful] stench filling his nostrils . . .

I’ve underlined the adverbial clause for you. It’s nonrestrictive in this sentence, so you should place a comma after the word later.

Paul Thayer