Dear Tasman Mouldey,
Good day! Thank you for posting to Microsoft Community. We are happy to assist you.
As per the description you have shared, we understand that you have a concern with Microsoft Bookings time allocation.
To better understand the issue and provide possible solution, we need more details from you, please kindly provide us the following information. Thanks in advance!
- Could you please provide us with the screenshot of the issue?
- May I please double confirm if you tried to change the default scheduling policy time increments? if not, please kindly sign into your Microsoft Bookings -->go to Booking page -->Default scheduling policy -->Change the default time increments to 2hr -->Save. Then, check if there is any difference. you can refer to the screenshot below.

I look forward to your response. Kindly note that the above requested information is required for further analysis and troubleshooting of your situation. Your patience and cooperation are much appreciated.
Thank you for your precious time. Have a nice day.
Sincerely,
Libeamlak | Microsoft Community Moderator