Is too much charge time bad for your iPhone?
Nah. Electricity is PULLED to devices that use it, not PUSHED from the plug. The phone is smart enough to stop pulling when its battery is full. 

EDIT: However, an adapter can provide incorrect voltage for a device. Don't take what I said there and wire your iphone power adapter to a 220 source, for instance. You can OVERDRIVE a device with too many volts, but you can't send it "too much" of the right voltage, because the amperage is a function of the device's draw. I know I just said that assuming that you understand the difference between volts and amps, but there it is; they're different.