Spring and fall are considered the best times of the year to hydroseed to ensure a good result from your efforts. These times of year generally provide the milder, wetter environments that are beneficial for hydroseed to establish and grow well. By contrast, because summers tend to be hotter and drier, hydroseeding in the summer can be more challenging. After hydroseeding, the seeds require a lot of water. This makes spring a good time of year to hydroseed, since it tends to be rainy throughout much of the seasons. As with any kind of planting, you must be very aware of the weather around the time you want to hydroseed - frost can be hard on grass seed, slowing down and sometimes even killing seeds, so make sure you're planning to hydroseed late enough in the spring so frost isn't likely.
With proper watering and fertilizing, you will start to see germination begin within 10-14 days, have a mowable lawn in about 5-8 weeks, and end up with a fully established lawn in about 6-9 months. Green dye will fade within 1-5 days. Keep as much traffic as possible off of the newly seeded areas for the first 6 weeks. At first, some areas will come in much better than others in the first few weeks, this normal and typical with all hydroseed applications due to differing amounts of sun, shade, and water. After 4-5 weeks as the lawn begins to fill in it is recommended that you scratch up the thin areas and seed some of those areas by hand to help everything along.