Specifically, after the constitution was instituted, or the war of 1812, did the founder's views evolve since they actually had to establish a central government and recognize the benefits of a standing army? Or were there already a large number of founders who understood this advantage? My understanding was that they generally opposed standing armies because of their experience with the British military being used tyrannically by the King. I ask this because president Washington's second veto message indicates that he recognized were advantages to a standing army as early as 1797.
Of course the founders understood the distinct benefits of having a standing army. (They were quite aware that failure to keep one would certainly lead to becoming a colony again, and for all of them, it would mean death as traitors if that happened.) While the revolution ended in 1783, the conflict between the British and the Americans wouldn't really end until after the war of 1812 (accepting that our relationship didn't normalize at all until the early 1900's). The British in 1780's and 1790's continued to fortify many of their forts, "steal" American sailors and ships, as well as their cargo, and refused to buy American goods for the express purpose of making it difficult for our economy to get started (we could still buy British goods though). While all of this was against our peace treaty with them, there was little we could do to enforce it, and even Jay's treaty in the early 1790's did little to alleviate the tensions (Hamiltons was more or less forced to admit that the British could keep taking our stuff, but please by nice to us).
In 1796, the aftermath of the French revolution led to war with Britain, and when the US signed Jay's treaty with Britain, France didn't take it as a measure of good faith with it's formal Ally and threatened to invade the US as well as beginning the practice of copying what the British were already doing to our ships. The fear of war with France at this time got so bad that the Federalist party passed the Alien and Sedition acts (effectively shutting down free speech) and fear became that there was a hidden french faction in the US attempting to recreate the French revolution here. On top of that, President Adams went off to increase spending on Navy and Marine corps to defend American ships (because why wouldn't he?) And ended up in an actual quasi-war with France in the Atlantic ocean.
Finally, the whiskey rebellion occered in the late 1790's, and while it was a small (though actually kinda scary sounding rebellion) Washington felt the need to mercilessly crush it with some 13,000 soldiers led by Washington himself.
The point is, early America was full of dangers both foreign and native, and there simply wasn't anyway the young nation was going to survive without a standing army, and every single founding fathers knew that from the get go.