Please run the engines in a bucket of water. This helps torque the gearbox and drive system. It also reduces any harmonic noise from the drive system being run without any back pressure.
On all 4 stroke engines, it is imperative that you cycle the engines through full warm up and then for about 15 minutes (quarter throttle). Let the engine cool down and repeat the same procedure 2 more times and check oil levels. During this process cycle the throttle and rev it up occasionally and back to idle. Once complete, a load consisting of you driving the watercraft at varying throttle speeds in longer durations and positions helps seat rings and wear in the cylinder and sleeve for a long life. I would not run wide open immediately to allow the rings to seat properly. Working the throttle up to 3/4 is fine when initially breaking in the engine. Honda engines do not technically need break-in, but it is always good to run the engine and make any throttle adjustments before you hit the water.
Check the oil level immediately and fill up to the upper level if needed. 30 weight oil works great in the warmer climates. Adjust weight if necessary depending on season. It is common for a bit of oil to be burnt as it will bypass the rings as it breaks-in.
Once you have a few hours on the engine, I normally fully drain all 4 strokes and refill them with new oil. Fresh oil is the key to engine longevity. Never run the engines on the low mark on the dipstick. Engine damage and seizing will occur. Protect the investment. Always check oil levels before and after every trip to maximize life on all size power-heads. Don't void warranties by being careless. No low oil shut-off switches are found on these small 4 strokes with the exception of the Honda GXV50 engine. The larger 5 hp and up vertical engines commonly have this feature and a much larger oil sump. The safe zone for all Honda and non-branded small 4 strokes is to check your oil every trip, and top off after a day of hard run time.