Their currently is no Install Parameter or Organization option for this. I just tested an entry in one of our test environments and was able to book 2,000 hours in one entry.
Nicolas is correct. So because of this we created a Flex to prevent this, but then found that the Flex would slow the system down (this was many years ago). So we then created an Inbox for the Sys Admins to monitor. We now sync with our ERP system, so hours populate to work orders based on the work order and number of hours being listed on timesheets - we now never have this issue of over booking (and users can only book in .25 increments).
Thank you both. I think I will make an inbox for this.