[gfs]

It sounds like you need an interview before the bigger interview. If the questions aren’t too in-depth, I’d say have a timed shorter talk with the candidate to weed out any you don’t think would be a good fit. Think of it as a coding exercise before coming onsite. I imagine this will save you time in the long run.

[AnimalMuppet]

I agree. But I'd make the pre-interview be over the phone. Whatever you ask them in the first ten minutes of the in-person interview, ask it on the phone beforehand. Only invite them for the in-person interview if they pass the phone interview.