As tiltrider1 states, best guess is when the models converge. But it really depends on what you're doing. Crossing a large body of water, or heading 70-miles up the ICW?
1. PredictWind has their own algorithm that interpolates each model. It's fairly well respected for offshore passage makers.
2. Both the ECMWF and the GFS core models focus on 3-5 day forecasts, not 1-3 day which is of much greater interest to the average recreational boater. As such, while either will generate a short term forecast, they are most useful for longer range passages or departure planning.
3. PredictWind, FastSeas (which uses Windy data) and other prediction and route planning are reasonably accurate - with many caveats. 72-hour forecast remains the limit for reasonably reliable (80% accuracy or so) forecasts.
4. If you plan to make a run of more than 24-hours or so, it really helps to spend a little bit of time digesting the synoptic charts issued by NOAA/NWS. These have human interpretations about predicted movements and intensities of high and low pressures that are invaluable. It gives you about 80% of the data you need to make an reliably informed decision, and to understand why Windy or PredictWind says what they say. Picking up buoy reports fills in a bunch more data. .