This is tricky to explain. Those type of alternator are intended for charging batteries. Once the speed is sufficient to exceed battery volts it starts to produce current. The faster you turn it the more current it produces.
Without a battery you will reach the 24v at the same speed but the current produced is a different matter, it depends on the load and if your load is an inverter then the current will depend partly on how much current the inverter will draw ( and that depends on its load). it also requires considerable speed from the alternator to provide the current through the internal resistance of the alternator.
You will probably find the whole thing unstable without the battery to buffer the load. Too slow and it will trip on low volts or it just won't supply the load. Too fast and it will trip on over volts unless your load on it matches accurately enough to maintain near 24v on the terminals.
One thing is certain, to provide 25A you will need a great deal of effort to turn it. A small wind turbine can produce several horsepower in a good wind, man will struggle to maintain 300W for any length of time.
