I suspect not even seconds, but as soon as it occurred to him.
The military option is always an alternative, it exists, the US president commands an impressive military force trained and equipped for every conceivable option, why not consider this option?
The US military trains for all sorts of missions and is standing by to execute them at all times, there's little need to move equipment or men in preparation for something as insignificant as intervention in Venezuela. North Korea could be a bit more challenging, though about 40,000 are forward deployed, trained and suitably equipped there already, with about as many more in the area.
Indeed, Trump needs to be explained the legal effects of this 'blurting' of his under international law, I don't think he appreciates this, am sure he would be displeased to find out about how context and nuance affect utterances by heads of state. It is very different in business. Really, someone should explain this to him.
I'm a professor of International Relations, I know this is important (and that few really understand how this works).