That will depend on what species you’re growing, the size of your logs, and environmental conditions. Most mushrooms on standard size logs in temperate climates will take about a year to fully colonize before they fruit. This can vary between 6 months to two years. Smaller diameter logs and soft hardwoods will typically fruit sooner, though they’ll have less longevity.
Often, mushrooms need cool weather and moisture to fruit. Growth slows in the heat of the summer. If you inoculate in the spring, you might get your first flush of mushrooms in the fall but most likely it will take a full year until you see your first fruiting. If you inoculate in the fall and are able to keep the mycelium from going dormant, you may get mushrooms as soon as the next spring, though more likely the following fall.