They mean different things. The first is poor English but could mean that the exam took place at some time during the day. The second is good English and means that the exam took the whole day, but it is not fully clear.. does it mean 8 hours or 24 hours?

Thank you everyone

As a native speaker the first one sounds a little awkward maybe, but everyone will understand you. The second one is better. I understand them to mean the same thing.

2nd one is clear.