April Fool's Day

This week's question: In the UK, we are traditionally allowed to play jokes on people until what time in the day? Is it:
b) midday
I'm interested in this topic because in Spain the Abril´s Fool´s Day is in a couple of days, on December 28, and someone always spend me a joke.
It have not cost me understand the audio side because I think is a fairly easy issue.
The Vocabulary from the programme was easy because the audio explain it well, I did not know the pronunciation of words like hoax and gullible.