If it happens only when cold, could also have a vacuum leak somewhere. For such a new ride, if it's definitely repeatable at-will, when cold after overnight stay, take it back to the stealership, and have them find the issue, by having them start it up first thing in the morning when they come in before the sun heats up things. 640 miles... sheesh.... loose hose somewhere that sucks air and causes a stumble until it seals up from heat expansion. Why bust your buns on it? Let them figure it out.
If it stumbles on first start, try this to see if it helps.... priming the fuel pump to build up pressure in the fuel line before starting. The pressure really shouldn't bleed off that bad overnight, but give this a whirl anyway:
1. Turn key on but not on start position, listen for pump noise, priming.
2. Turn key off, wait 2 seconds, turn key on but not start position, probably won't hear much as fuel pressure has built up
3. Do the same thing a 3rd time just to make sure pump has built up pressure.
4. Start the car, and listen for the stumble. Could be an initial fuel delivery/pressure issue, transient in nature once pressure builds up.
Still should take it in since the pressure shouldn't bleed off that badly unless the car sits for a way-long time.