I disagree with Auteck's recommendation, and I'm a little surprised he recommended what he did. Your original grass seed mix selection was tall fescue, fine fescues and KBG. I suspect you have mostly tall fescue growing since you have bare spots. If the KBG in your original grass mix had germinated fully, then it should fill in bare areas in the sunnier parts of your lawn. I agree with him in that perennial rye is usually what is grown in your area, but there was no perennial rye in that original mix. Overseeding your lawn with it now will give you some throughout the whole lawn, but the bare spots will be all PR, and they will stand out against the TF you have now. My advice, use either all TF to overseed, or a mix that has similar percentages to your original mix. I would also stick with Pennington's as it is usually the best mix in the big box stores.

I got a commission for the Appian Way, so that's on the easel right now. And a lot of cypress. :-) Mostly, my natural instinct is to follow the season itself, so snow when it snows... The great thing about all this is when guests walk in, the wall paintings are always different. :-) If you don't like what you see, come back in three months. So while we're due for yet another punch of a three inch storm tomorrow, I'm mixing bright and dark greens, sun-warmed grays and working with ruddy Titanate off-whites. Overseeding would definitely be best done in fall, but if you have to in spring, you have to. Just be prepared to coddle that over summer. In that case, you can use Mesotrione as a pre-emergent, or Tenacity (they're the same thing). Sprayed Tenacity will take out a fair percentage of weeds, and keep weeds from sprouting in those locations for about thirty days. It's not easy on fescues, but they'll survive the experience and sprout through it, but they tend to whiten a bit. While a bit ghostly-looking, they'll recover. Starter fertilizer with Mesotrione, if used when overseeding, keeps the weeds down for 30 days during the overseed period. It's not perfect, but it does certainly help, and it's the only pre-emergent you can use with northern grass seed. I do wish they'd make it available without the fertilizer, which new grass doesn't really need, but the only other option is to spray with Tenacity (which would actually be just fine and I recommend that instead if the person has it).

I overseeded my crappy lawn which had a ton of damage from crows and skunks digging up chafer beetle grubs in very early spring. I overseesed with a fescue/rye/bluegrass blend about a month ago after spreading a thin layer of top dressing that had sand and manure mixed in. I applied starter fertilizer a week and a half later and it's all looking great right now. Has almost filled in the bald patches. I have had some weeds, mainly mouse eared chickweed but have so far been able to keep in check with hand pulling. I say go for it. You can always do a more ideal repair in fall as I plan to do. Here's a before and almost after. Still some filling in to do but so much better. First photo about a month ago second and third photos from this morning and last night. I plan to follow up with some alfalfa or soybean meal soon and stick to organics if I can. You wont find soybean or alfalfa at big box. Try an agricultural supply store. I'm in the city and have to drive to burbs to get mine.

If your prevailing wind is from the shore, then I'd say any time would be good. If your prevailing wind is from New Hampshire, then I'd wait until the end of this month. Earlier is better as long as you don't have temps in the 90s day after day.