Like @Walt, I use a magnetic stirrer, which gives my juices a thorough blending, generates heat through agitation and general chemical exothermic reaction, and greatly reduces a need for steeping. Mostly, I mix my juices weeks before I will use them, so they do get plenty of "aging" time on the shelf before they are used, but they tend to taste the same the day I mix them, as they do months later....
Recommendations on heat work well, but be careful not to overheat them as they will become dark and the flavor can be harsh. Chocolates and custards do tend to get better with age, regardless.