The amount of time you spend on the drops is fairly irrelevant - the type of riding you do, the terrain you're in, the conditions you ride under, the amount of tight cornering you have to do all have big influences on the amount of time spend on the drops. What's much more important is how comfortable you are on the drops which is more important. If you feel comfortable on the drops when cruising along at no effort level then you need to lower your handle bars, a lot. If you can't get onto the drops even when absolutely hammering it on the flat or as a sprint then they're too low.