Its all about the soil temps.
Carrots need at least 45degF, 65 is best...
Nebraska soil temps are more like 34degF according to
https://www.weather.gov/ncrfc/lmi_soiltemperaturedepthmaps
If you have a lot of seed to spare, go ahead, it will wait for warmer temps. You can speed up the warming with cloches, clear plastic, temporary cold frames, etc. The only danger is seed will rot in cold water-saturated soil before it can germinate so factor in your soil moisture and rain forecast.
Garlic can be planted anytime from August to April in your climate. You probably have cold-acclimated phenotypes, but some extra mulch before hard freezes are a good idea. My elephant garlic got a little freeze damage on the outer leaves, Music hardneck in a more protected spot survived 10degF unscathed.
My garden will attract every herbivore in the neighborhood to come feast on any early plantings, so I have to cover with wire cages weighted on the edges with rocks and an apron of wire 1/2 meter out to prevent groundhogs digging under.