The rules indicate a Disguise normally takes about 10 minutes to put together. You also don't have any props. However... this is sort of "what the Goblin King does" kind of ability, and I don't want your character to not be able to do the kind of stuff he was designed to do.
So... if you use your Illusion Power attached to your Spheres, you can conjure props, and bypass the need to prep. Normally, each of "no props" and "no prep" would give you a -5 Penalty (total -10). As it happens, Jareth can still pull that off with a bonus, even if he doesn't use Illusions.
In the future, you might want to add: Master of Disguise Quickness 6 (Limited to Disguise), Improvised Tools (limited to Disguise) [2pp]
You could also Power Stunt a Morph off of your Illusion, or even your Barn Owl form... but that will cost you a Hero Point.
It does occur to me that Jareth is having another Complication. He doesn't entirely know what things are. He recognizes that the guys in black are warriors (which, by the way, means they're not like Mall Cops, they're full fledged combatants). But... he couldn't say "oh, they look like SWAT, they look like Mercs," etc. He recognizes that they are carrying weapons, but he's not really sure what the difference between a rifle, a shotgun, an AK47, etc. are.