Its safe to say it will take around half the day, because:
They will show you around the pharmacy department/ inform you about the course structure, show you the accomadation, give you a tour
and also do your interview!! so it's a whole day thing..
The interview is fine, just be yourself and try answer everything to the best of your ability. They will ask a few science questions (e.g. related to what you've studied so far, and why its important - also they will ask simple maths questions, e.g. converting units/working out percentages etc)
This is what happened last year when i went there for an interview.