I see where you might be confused. If you look at the tycoon's description carefully, it doesn't say 'reduces production time by 50%', but rather something like 'increases production rate by 50%'.
So you start with 100% production rate and 8h production cycles,
1 tycoon will boost this to 150% production rate and 5.3h cycles ([1/1.5] * 8h),
2 will further increase it to 200% production rate and 4h cycles ([1/2] * 8h),
3 get it up to 250% production rate and 3.2h cycles ([1/2.5] * 8h)
and so on...
you'll need 6 tycoons (400% production) to get to 2h production cycles.
“All warfare is based on deception. Hence, when we are able to attack, we must seem unable; when using our forces, we must appear inactive; when we are near, we must make the enemy believe we are far away.”
― Sun Tzu, The Art of War