Oh, that's great! My main suggestion would be to pre-determine which skills the Detective will have, by picking out which Archetypes you want to have available for players - possibly skip Expertise, as well. How many players do you expect to have? If it's 5+, you can predetermine which 2 skills each archetype will bring to bear, so there's less choice/overlap.
I'd also try to have the initial scenario the Detective is in be relatively rich with stuff to engage with, and some big discoveries to make early on, since I assume they're unlikely to get terribly far in the Case within the time available. But, I don't know - I haven't run a convention game, so I don't have a lot of comparison! Godspeed!
I'm happy to give suggestions on any tweaks or ideas you have, just reply here and I'll try to get on them ASAP.