Hi Lava,
I only skim this thread from time to time. Just my opinion but if you are going to overseed you should do it ASAP. Everything slows way down, wasn't it last fall they hydroseeded too late? If I were going to plant grass I would have done it a week or two ago. Longer night and less sun angle starts cooling the soil. Yesterday was the first day I mowed down to 3.5". Normally I mow at 4" all summer. Nights in the 40's will be common soon
Good luck