Between us and Ha-Shem, and given the broad times that are allowed for most things, it seems Ha-Shem is very laid back about time – several hours to say Shma, you can Mekabbel Shabbos hours early, and don’t have to end Shabbos until well after the the zman.
Otherwise its a matter of timing. Germans and most Americans tend to be punctual. Many other cultures consider arriving strictly on time to be rude. East European Jews tend not to be fanatic about punctuality, and many other cultures have a similar attitude towards time. As a practical matter, its best to figure out the custom of those you deal with, and not make an issue about (again, other than when it is a matter of halacha).