u/Polciu

Hi everyone, I'm new to the industry I'm starting on Monday for a month contract PAYE with possible extension. I have things booked for my sons birthday on Friday 29th May and wanted to take it as a day off - at what stage do I ask for it? I'm worried it'll give the wrong impression if I do it too quickly at the same time I don't want to leave it too late. And also do I ask the agency or the site manager. Ta