You can set the Bypass flood check user group permission for your user group.
I'd recommend that you limit the members who have this user permission and don't give it to the Registered group which everyone should have as their primary user group. It's good protection against any spammers who manage to register and post as it limits how many posts they can make over time. Some admins who give this permission to everyone can find spammers making thousands of posts in a very short time.
I'd recommend that this is left at the default of 30 seconds and give the bypass flood check permission to a small number of trusted members or just to staff. Setting it too low leads to spammers posting more before getting caught.