It depends on whether your meadow is "meadow" or "pasture".

There's two alternatives - you can cut from about now, then continue to give it infrequent longish cuts till the end of the year. This will allow early flowering plants to flower and set seed, and in particular helps things like primroses and cowslips which don't really like spending most of the year under long grass. This is effectively "pasture" - allowing grass to grow early in the year, then letting your "animals" graze it.

Or go for the "hay meadow" approach - let the grass flower, and cut once all the flowers are seeding - for me this is sometime in September. This will allow the flowers that don't flower till June or July to flourish.

I'm doing both, on a rather shaded damp site, and gradually finding out which flowers prefer which. My "pasture" is at the moment full of buttercups and the orange hawkweed, but is relatively tame. My "meadow" is almost thigh deep, with melancholy thistle, salad burnet, field geranium, 3 different vetches, meadow vetchling, birds foot trefoil, hardheads, and yellow rattle. So at the moment it's the more attractive, but in spring the "pasture" is full of primroses, cowslips, daffodils, snakeshead fritillary.