Satellites can detect a launch, but if the launch is very close to its target it's still difficult or impossible to react in time and defend against. Maybe the US has some new secret tech for that we haven't seen yet, but based on what we know publicly it doesn't. As you mention, Hamas has shown you can overwhelm expensive missile defense systems with quantity of cheap rockets, though the distance from Cuba to the US is much greater and that wouldn't work as well there.
> friendly ness is way better to counter.
That's what everyone believed in the 90s and why the US policy establishment pushed to integrate China and Russia and others into the WTO and global economy. But they now know it's not universally true. It works with some countries like Vietnam, but failed with others like China and Russia. It now depends on the particular circumstances of each country. Cuba's circumstances are that it's just too close to the US for comfort, and with a history of threatening the US with nukes. So there won't be any policy of friendliness toward Cuba unless it renounces single-party authoritarian rule and fully democratizes.
You realize that it is only for the, what, top 0.001% for which the exact flight time has any relevance, so that they have time to hide and spend the next 200 years underground belittling us for not being war mongers enough.