The leaves of autumn crocuses are almost wholly yellow now. (These are the true autumn-flowering crocuses such as Crocus speciosus and C. nudiflorus, not to be confused with the larger Colchicums.) C. nudiflorus comes into leaf in December and has already fed and nourished its corm by early May. So if it is naturalised in grass, the turf can be close mown from mid-May onwards without reducing the flowering potential.
When the grass slows down in September and October it should be left a bit longer to support the flowers, which appear before the leaves. Snowdrops can be mown over in May, and are perfectly happy in turf. So is Chionodoxa sardensis, that richest of early blue bulbs. The three bring colour to the quiet seasons yet allow you to mow as short as you wish through the summer.