That's a _lot_ further down the path of "intent to create a bomb hoax" than "building a clock".
(And personally, I'm of the opinion that putting a schoolkid in jail for what Woz did was ignorantly overreacting... Quite possibly because I was that same kind of schoolkid who'd make that same silly decision. Hell look at my Flickr photo's comment - I thought it would be hilarious to do that at 43 years old, it's just experience and perspective that stopped me building exactly what Woz made...)
Depriving someone of their liberty, even for a few hours, is a big deal. That's why compensation for wrongful arrest runs to $5,000 - $10,000 per hour.
In cases of bomb threats and security breaches, qualified immunity is going to provide significant leeway when dealing with IEDs. Since most high-schools have strict anti-weapons rules, you can get arrested for a swiss army knife. Again, this is not the same thing as an apologia for a perp walk of a 14 year old. But if you want to see a "false arrest" look at what happened to the Blake last week in NYC. That was an unreasonable takedown of a private citizen with no effort made to establish identity; and a violent arrest for a non-fleeing suspect in a non-violent crime, etc.
In this case you are dealing with an "IED" vs an "Improvised Timekeeping Device", and since the former often includes the latter as a component part, its not completely baseless. This is why you cannot fly with liquid water on an airplane--the security forces cannot distinguish (on-sight) "legitimate water" in a clear bottle from several chemicals (aslo clear) than can be combined into an explosive IED that will puncture a pressure hull of an airliner. If you insist on taking your water through security you will get it removed or be arrested.