Re: Tiny time jump
If the party scene is in a completely separate chapter then I can't see any problem at all, as I think we automatically re-programme our brain, time-wise, at chapter breaks, so any jump is accepted, as long as it's made clear.
If it's a continuation of the same chapter as the I'm-going-to-a-party scene, which I think is what you mean, then it's not quite as easy, but it's still preferable to some alternatives eg writing some kind of filler scene to bulk the first out.
The first scene, though -- what does it do apart from tell us he's going to a party? Is that its only function? If so, I'd be tempted to dump it. I'm a much more convoluted writer than you, so putting in a bit of explanation at the party itself wouldn't worry me, but I think you could equally well give the information in an earlier scene between them -- after all, these things are known weeks/months in advance, so he could have been worrying about what clothes to wear/who he's going to have to sit next to for the last week or more.