Presumably you are restoring a pre-existing iCloud backup to your iPad. The time required to restore the iPad will be determined by many factors, including but not limited to:
- how much data must be backed-up to iCloud
- the speed/throughput of your internet connection
- the speed/throughput of your WiFi network
- server loading; assuming an iCloud backup, Apple’s regional servers may be busy
The only aspect that you may be able to directly influence is your WiFi network. You should note, however, that the slowest item in the chain will ultimately be the limiting factor.
Keep your iPad connected to its Power Adapter throughout the restore process - as this will keep the WiFi connection active. The restore process should continue to run in the background.