Its rarely too late to plantclover - especially in northern states. The first year of a clover planting is often a "building year" with little forage production. Most of the clover's 1st yr energies are towards root establishment. I'd plant clover now if you have time. Ultimately - Rain at germination and the 1st 4 weeks makes or breaks a clover plot. I'm still planting clover - planted some Sunday April 30th - I'd keep planting clover another 4 weeks here with a good seedbed. and no previous weed establishment.

FH