Hi there, @Dart_Scooter 
At the moment, custom duration can be set in minutes only. I am really sorry!
However, I agree that it would be awesome to set the duration in hours too and I’ve added this idea to the Wishlist on your behalf 
- Custom duration in hours
To hide a duration, please use this CSS code - Hide duration
Keep in mind that this code will remove the duration from the widget only, but it will be displayed in the booking confirmation emails.