My opinion: be aggressive at the plate; It's not a typical game situation. Coaches are there to see swings.
as far as the 60, not sure how coaches use the time recorded there. My guy has run a 6.75 at a showcase, but I timed him at 6.63 in practice, so he's gonna try to beat the 6.75. If he runs slower, he's gonna ignore it when he sends out his emails/letters etc. If he beats it, he'll tell everyone how much he's improved.
Is your boy in the academic tryout? If so, he'll have a chance to run it then, too.