while some folks consider it reassuring to see such quick activity, the "lag" time is actually a very productive time for the yeast, it's their time to absorb 02 and get geared up for the exponential growth phase. while such quick activity can mean that you did a good job with pitching rates and numbers, you have to be very confident in your methods. a pitching rate that is optimal and using pure 02 (unless you feel like rocking a carboy for 20 min) to aerate are circumstances that would make such quick activity a real party.
this is all being said from the standpoint of what is absolutely optimal. i wouldn't really sweat any of the above unless you find that the finished product is faulty is some way, that's when the diagnosis begins.