Comma usage

English as a Second Language English Vocabulary, Grammar and Idioms
1

This sentence is grammatically correct: “At this time of the year the Netherlands is one hour ahead of the UK”.

I don’t understand of why a comma is not used to separate the the introductory clause of that sentence into “At this time of the year, the Netherlands is one hour ahead of the UK” ?

2

Some people would use a comma there and other people wouldn’t bother. To me, both styles are acceptable.