2 days ago, I put down 2 pallets of centipede sod in Lexington SC. Have watered each day. Now we have two nights of below freezing temps coming up - mid-20s F. Should I attempt to cover the grass or just let it be? Thanks.
The cold snap is not going to kill it. The sod will go dormant soon. It will lack the roots needed to protect it's self from a deep freeze, but a cold snap will not kill it. Best possibility is you get a long rainy winter. OR you get really deep snow pack to insulate it. Then in spring it will start to root and grow. Otherwise, you might get some die off in spots, but overall the sod will survive. It might be slow to break winter dormancy, but it eventually fill in any of those dead spots.
If you do have dead spots in the spring, ask for a partial refund. If they installed the sod for you, have the come out and do the repairs, if any. I think it will come through the average South Central South Carolina winter just fine.
I grew up and lived most of my life between Virginia and Georgia. I know that overall winters have been milder wetter in that region than they were just 20 years ago.
The basic problem is that apart from your immediate cold snap, the average climate will be too cold for the grass to really establish itself until about March next year.
As a rule of thumb, grass doesn't grow much when the minimum night time temperature is below 50F (10C) though of course the temperature has to be much lower to actually kill it.
If you wanted to returf the lawn before winter the best time would have been about September, to give it time to get established before winter, or wait until spring.
Covering the lawn for a long period of time is guaranteed to kill it. Nothing can grow without light. Leaving it uncovered is probably the best you can do.
I'm not going to ask why somebody sold the turf to you at the wrong time of year - but hey, they won't mind when you have to buy another two pallets next spring to try again!
While the grass may not establish itself well until next spring, the sod is susceptible to drying out since the root depth is very shallow. Best insurance is to keep the sod moist, and ensure that it is fully in contact with the substrate soil. You can achieve this with a light roller, and occasional irrigation when the weather threatens to dry out the sod with little rain and persistent wind.