I just got done reseeding a few spots that didn't take well. Most of the time you aren't gonna get full germination, especially if homeowners have to work and find the right day and time to reseed again. I'm seeding 12k and you can find a lot of spots that don't take in that area. My take on it is if I see areas that are not germinating, then i want those areas to be seeded this year before the window closes for the fall...not wait until spring and lose most of that seeding from heat in summer. You should still have enough time to get some seedlings going if you don't wait any longer. Just my $.02

So long as the ground stay warm (i.e, above 60 degrees) you can get germination through October. Depends on the seed. Keep in mind that sometimes it is easier to seed shady areas in the spring because the trees haven't fully leaved out and shady areas are less prone to weeds to tupersan will be OK (vs. Dimension or Halts). I would keep re-seeding, last year I did the same thing, once a week I would throw down more seed (with some peat moss over it) up until the end of October.

I think your issue will be that now (mid-September) is the time to be starting grass in zone 5. If you let it go too long, it will be late in the season and it may not sprout this fall or not have developed enough roots to survive the winter. Spring sprouted grass doesn't do as well (cold soil and warm to hot air) and there are the annual grasses to compete with new perennial grass, and before it's warm enough to sprout you may have issues with seed washing away in the spring snow melt and rains. So if there's any way you can get the area watered on a regular basis you will have better success with the grass starting it growing now or in the next week or so. In one spot you mentioned water hook up and in another irrigation. Can you do regular sprinkler watering before the irrigation system goes in? That is, is there any water available and are there functioning outdoor faucets? How large an area is it? How likely are you to have regular rain? Can you set up some type of water collection system like rain barrels if it's a smaller area that needs watering?

When you seed new grass in the spring you always (Always, ALWAYS) get crabgrass. There is no way around it. Why? Because spring is the only time of year that crabgrass seed germinates. You are literally begging for crabgrass when you seed real grass seed at the same time the crabgrass seed is germinating. Furthermore, any fescue, rye, or Kentucky bluegrass you seed now will not have time to develop the hardy roots they need to survive a hot summer. By July you would have a full crabgrass lawn. Your problem with crabgrass developed last summer. If the lawn is not very dense at this point, the best thing you can do is withhold moisture from the crabgrass seed. Do that with deep and infrequent watering. More on that later. Of course Mother Nature may have other intentions and give you a nice slow soak over a 4-day period. If that happens you're going to get crabgrass. Preemergent will help. You can apply when you see the first forsythia blooms or with the first rains of spring. Then reapply if you get another rainstorm later in the spring. Apply during the rain if you can. Timing is everything. Nutsedge is a swamp type grass, so I am guessing you either had a lot of rain last year or you over extended the watering style needed for seed germination past when it had all germinated. Mow at your mower's highest setting to help shade the soil and block the sunlight from any newly germinated weed seeds. This can go a long way to keeping out the low growing crabgrass. It also develops deeper roots to help survive the heat of summer. Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.