Late Fall. The Lupinus texensis (Texas bluebonnet) are probably already up, preparing to bloom soon and then go to seed in the Summer. If you absolutely must mow now, you will sacrifice the seedlings for this Summer's growth, blooms and seeds for next year. There will be some residual seeds in the soil which will probably sprout next year, and they will likely do better without all the shade and competition from the grasses. However, if you mow now you will lose this spring's bloom and therefore this fall's seeds and should not expect much next year. You might even have to reseed - you really need to let the plants do their own job of seeding.