Swapping out F250 Yamaha for BT350 Honda

Congratulations!

You may wait 10-20 hours before you check in depth the fuel economy, it can be that the engine runs richer fir the first hours of the break-in period.
The on a flat and safe stretch of water write down rpm-speed-fuel flow in 500 rpm steps, this will help you greatly with understanding how well your prop is working.
BTW: What prop is installed, the original Honda one?
Chris