I have a patch of Colchicum, courtesy of the previous owner. It makes foliage in the spring, dies back in summer, and then flowers in the fall. Flowers look like crocus.

I don't know that they would be suitable for the lawn because you would likely need to mow it by now, and the foliage is still quite robust, has not started dying back yet. Also they may not be vigorous enough to compete with turf grass.

There is confusion that could be caused by the use of common names here. Colchicum is sometimes called autumn crocus. It has flowers that are bigger than real crocus IME that's much pinker in color, and foliage that is larger than daffodils that behaves as terrene described. Here's Brent and Becky's page on Colchicum.
https://store.brentandbeckysbulbs.com/spring/genus.php?genusid=11

There are crocuses that blooms in the autumn that are real crocus, with the typical delicate blue-purple or occasionally white flowers.
https://store.brentandbeckysbulbs.com/spring/genus.php?genusid=13

In my experience, both will bloom the year they are planted.

The only autumn daffodil I could find is Sternbergia lutea, which Plant Delights Nursery lists as only being hardy to zone 7, so I don't know anything about it since it's not hardy for me.

Oops, I didn't answer all your questions.

I probably wouldn't plant fall-blooming crocus in your lawn because unlike in the spring when cold soil causes slow growth of grass, the grass is growing quickly in September and will need to be mowed when the flowers are setting buds. While they are technically perennial, the critters may eat them just like spring crocus, so in reality they rarely come back for a lot of years in my garden since the voles get them. Because I love that color in the fall, I plant them anyway, usually around plants that the voles don't like

Colchicum needs to be planted in a flower garden since the foliage is so large and coarse. They tend to be expensive per bulb, but they are toxic to critters and will multiply over time, so if you like that bright purply-pink color in the fall, I think that they are worth the money to buy a few of the less expensive ones. I bought a few and now have several very large clumps of flowers each fall after less than 10 years.

here is a link from the Brecks web site for what they are calling autumn daffodil - which looks more like a crocus than a daffodil to me.

http://www2.brecks.com/topaz-autumn-daffodil/p/84637/

And here are links for the 2 Fall crocuses that Brecks sells

http://www2.brecks.com/fall-white-crocus/p/84636/

http://www2.brecks.com/fall-white-crocus/p/84636/

Maybe I'll just order 1 (I think they are all 10 bulb quantities) of each and see how they do. Will pick a spot in the garden - will forget the lawn idea.

Still looking for additional insight.

pixie lou,

I ordered both Fall crocus (Crocus) and Autumn crocus (Colchicum) from Brent & Becky's. Colchicum are much bigger and have huge leathery leaves that come up in Spring and then die away before the flowers appear. Then the flowers come up in the Fall with no leaves. Many look like giant crocus flowers but there are some like Colchicum 'Waterlily' or 'Pleniflorum' that are double. Fall crocus are just that... crocuses that bloom in the Fall. I really enjoyed them last year; they were much smaller than Colchicum, but lovely in a group. Both kinds were shipped in late Summer and bloomed the same year in the Fall.

And I think nhbabs is right about Sternbergia lutea which does look exactly like a Fall blooming yellow crocus. White Flower farm lists it as hardy to Zone 6.

I did end up ordering both the fall blooming crocus and daffodils from brecks. They arrived earlier this week and I planted them this morning. Now it's wait and see what happens!

It is 10 days later and still no sign of foliage on any of them. Hmmmm. Patience is not my strong point.

I have these in my yard, amongst the grass. The previous owner planted them years ago. They've naturalized and look great! Perhaps they won't work well in everyone's yard, but it's worth a try. Just don't invest too much in the experiment.

Pixie Lou -

Don't expect to see any above ground growth this fall on the daffodils. They are working on growing roots now, and will put out foliage next spring. The crocus should bloom but IME they are later than ones planted in prior years.

I ordered and planted Colchicum last fall, and was disappointed that nothing came up. This fall, surprise! They appeared. It could have been the harvest, the weather, when they were planted. But they survived and bloomed in spades.
Be sure to mark the bulbs very clearly and don't move the tags as you dig next spring. Or you'll slice and dice an expensive purchase. The colchicum I planted two weeks ago are blooming.
Idabean

I actually got 1 little bloom. This is supposedly the autumn daffodil. Though it looks more like a crocus to me.

I have the 3 groups of bulbs marked. Hopefully my patience will pay off and I will get a better show next year.

ooh - one of the crocuses (or is that croci?) has bloomed! and there are 3 or 4 little blossoms sticking out of the ground!