SV,
Your ideal PH should be somewhere around 6.5 to 6.8. Limestone will raise your PH, but works very slowly, especially in clay soils. I've heard that hydrated lime works a little quicker than the others, but will still probably take months. Also, if your soil needs magnesium, dolomitic limestone contains this, and will raise your PH also. It won't hurt to add limestone now(use recommended amounts), it will definately leave your soil in better shape for next season. Check your PH again in the Fall,to let you know where you stand.