How long should a charge last. I have a new iPad Pro and it needs to be charged after 5-6 hours. Is that normal

Without a better understanding of your usage, a definitive answer is impossible to provide.

Apple quote a battery life of up to 10hrs with a long list of caveats. If your screen is operating at full brightness and running a graphics/CPU intensive task, then the battery life you quote is quite possible.

To add some context, my own iPad Pro 10.5” models regularly achieve 7-7.5hrs battery endurance before requiring recharge - typically operating at 30% screen brightness and a sustained average CPU load of ~15%.