Yeah you only need smart casual for your arrival and for breakfast the day you leave.
Some friendly (old man) advice on this. First impressions last.
Keep in mind that as an early 20s-keen-young-go-getter, your idea of what "smart casual" is,
may be somewhat different to the more mature (read "older") people that will be assessing you.
Dress to impress this "older" generation, not necessarily that of your peers.
For guys, I would recommend trousers and a collared shirt (not a polo shirt).
I say this because I've had some feedback from some people involved within the ASP that some of the candidates were dressed like they were going out on Friday night with their mates.
They do notice this stuff, so give yourselves the best chance - certainly what you wear does not reflect your abilities, but it does reflect your attitude to the process, especially in the minds of the "traditional-type" people potentially assessing you.
Disclaimer - I have no fashion sense - my wife tells me so...
Extra Disclaimer - I've told my wife what I wrote here and she reckons I'm an old fashioned loser.