From your previous lawn related questions:
Unless you correct me, I'm going to assume you have a cool-season lawn, therefore I believe you will find the following helpful/useful:
What's an organic way to discourage crabgrass from a large "lawn"?
Around "Labor Day" (beginning of September, early Autumn "Fall") here in the US, I prepare any bare spots for reseeding. Reseed using an appropriate seed for my lawn type. Cover the whole lawn with ½ to 1 inch (12.5 to 25mm) thick layer of STA-certified compost (bought in bulk locally). Water as needed, ie Amount needed for good germination to take place.
Reseed in early Autumn (Fall) ie Performing major cool-season lawn maintenance at this time of year, will give you the best results (reap the rewards the following cutting season).
How do I know when and how much to aerate my lawn?
On clay- or silt-type soils, or any turf receiving constant traffic, soil sealing and compacting can seriously impair turf growth. Grass roots are injured because air, water and fertilizers cannot reach them in sufficient quantities. Mechanical aeration to break through this barrier is essential for continued turf health. Fertilizer applications following aerification most efficiently provide nutrients to the turf roots.
Aeration is best done by power equipment that pulls out small cores of soil, or by cutting vertical grooves to provide openings every 3 to 4 inches. Power equipment is usually available at rental stores. Lawn-care companies may also provide this service to their customers.
Aeration should be done at least once a year where compaction is a problem. Early fall is the best time for bluegrass lawns, but aeration will be highly beneficial anytime the grass is actively growing, except possibly during midsummer heat.
How to tell if my lawn needs to be dethatched?
Lawn Dethatching tools
Today (2011-09-02), this "News for Missouri's Gardens, Yards, and Resources -- Volume 17, No. 9 -- September 2011" landed in my inbox, of interest to yourself (assuming you do in fact have a cool-season lawn) is the PDF:
Core aeration is a practice of pulling soil plugs to open the soil surface for better air exchange and nutrient and water movement. It is a practice that also helps to reduce compaction and thatch by spreading soil plugs on the surface. Soil plugs are crumbled and fall freely into aeration holes as well as spreading some soil into the thatch layer where soil microbes can feed on thatch debris. Aeration is a practice that can be done in both spring and fall but is the very best way to begin fall seeding and fertilization. Applications of fertilizer after aeration will move nutrients immediately into the root zone of your lawn. This practice has shown excellent results in the density and color of cool-season turfgrasses on their way to recovery from summer stresses. Spreading grass seed after aeration is also an excellent practice in lawns that have thinned considerably from summer pests.
Q. Is my thinking here correct?
A. Your thinking is ok! and makes sense (at least to me). In the US, the optimum time for cool-season lawn care is said to between 15th August and 15th September. Exact date is dependent on your location, "generally" speaking the further North you are the earlier you want to tackle cool-season lawn care...
I was planning to do my cool-season lawn care maintenance program this coming "Labor Day" weekend, but with temperatures of +100°F (+38°C) forecast for today and the following two days, there is no way I am going to further stress my lawn this coming weekend. I might do it the following weekend (10th - 11th Sept), but looking at the long range weather forecast, I'm thinking the weekend after that (17th - 18th Sept) would be better. As long as I can get out there and get it taken care of before the end of September I'm not too worried when I get it done...
Q. Should this core aeration and seeding be postponed for a few more weeks (into mid/late September)?
A. I would wait until the lawn has had a chance to dry out a little bit. Also if the temperature doesn't suddenly drop too much, anytime through September should be ok! Do keep in mind, the earlier you can get it taken care of in September the better (IMHO).
Q. When are the "best" and "acceptable" times for these fall services?
A. See above, and also follow the links I've posted above, as you will find a lot! of relevant and useful lawn care information by following them (IMHO).
Below information comes from Rutgers New Jersey Agricultural Experiment Station:
What to do? Dead lawns need to have the soil re-covered. Now is the best time to reseed a
lawn. The cooler air, warm soils, and more frequent rain of August and September present ideal
conditions to seed lawns and ensure establishment.
Tall fescue is a very good choice if you can seed before September 15th while perennial ryegrass, fine fescues, Kentucky bluegrass can continue to be used later in the fall when the soil cools.
Aerating and dethatching the lawn before seeding is very beneficial. Seed falling into the
openings created by aeration and dethatching is more likely to establish because the seed and soil contact is improved. You can also spread a light layer of compost over the lawn after aerating and seeding. Compost acts like a mulch, retaining moisture for the seed. Compost also adds nutrients and organic matter to the soil, both of which are beneficial to the survival of your lawn.
If it turns out, you do in fact have a warm-season lawn, the below information should prove useful to know:
Core aerifying can be done anytime the grass is actively growing. For cool season grasses such as bluegrass, fescues, and ryegrass, the best times are March, April, and September. Aerifying should be done before fertilizing, seeding or applying crabgrass preventers. Warm-season grasses such as Bermuda grass, buffalo grass, and zoysia grass, can be aerified from late May through July. It is important to allow at least four weeks of good growing weather for the plants to recover and fill the open aerator holes.