There are threads discussing ultrasonic steeping and magnetic stirrers. Both will reduce steep times significantly. I normally work well ahead but once in a while either don't or want to try something new without waiting. I use an ultrasonic cleaner and usually run a bottle through four, 30 minute, cycles. My normal steep is in a bottle, on the shelf, for two weeks with no outside agitation at all other than a good shake when I'm done mixing.
Nicotine and flavors both start to degrade as soon as they hit air. Heat makes them degrade faster, especially excessive heat. If you do use a method with heat keep it under 110F to avoid too much degradation when steeping.