I was going to make the same comment. I think hiring is the most important thing a company can do. I've worked for companies where they do pretty much everything else wrong, but they were succesful because they had good people who made things work. I've seen the total opposite also.
This is particularly so with programmers. A fantastic cleaner might be twice as fast as a pretty average one. But a great programmer can be tens of times faster than an average one, and will write more reliable and scalable code to boot. You are talking about hiring someone for years. If you can't justify spending the best part of a day with a handful of candidates then you are doing your company justice. If you get that great hire they will more than have repaid the time you invested within weeks. Then as they get more experience in your job they will become more and more efficient. For 40-50 hours a week. It doesn't take long for your initial investment in time to pay for itself.
People seem to have this attitude that you read resumes, maybe have a phone interview and then spend 45 minutes in an interview. That's how it's always been done, so it must be right. And only Google and Microsoft are big enough to warrant full day interviews. Because they have teams of people.
That's crap. They spend the time because they know it's vital to their business. And that's no different if your a 3-man company.
Now, the time has to come from somewhere, and other tasks don't stop existing just because you're interviewing. I agree this is a problem, but it is a separate issue from "should we spend a full day interviewing?".
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