Lime can be applied to the lawn any time of year but fall and spring are the best as that is when rain will wash the calcium into the soil. How quickly the lime works is due to what form and type you use. In Western Washington where the soil is naturally acidic and thus a great home for moss and buttercups it can take up to three years for annual applications of lime to make a difference. Buttercups need moist soil to thrive. A quicker fix is to dig out the buttercups and fill the area in with quick draining loam or sandy soil raising the soil level if you find you have moist soil due to a high water table. Great soil grows great lawns and the overabundance of weeds is teaching you about your soil. Keep growing, Marianne Binetti