Unless your iPad (or iPhone) is connected to power, the WiFi is programmed to turn off a certain amount of time after the device is put into Sleep. This is a battery-saving feature designed by Apple and can't be changed on a stock iDevice.
However, it shouldn't take 30 seconds to re-start the WiFi. Have you checked your router settings? Or, maybe try to "reset Network Settings" in your Settings app? You'll have to add in all your WiFi spots (to include putting in the passwords), but still, maybe it'll help?
Marilyn