Fastest SD card has ~300MB/s read speed and ~250MB/s write speed. Assuming you can write to those cards in parallel, that means you’ll need an additional one hour to write the data to the SD cards and another one hour to read them back. So 4 hours in total which halves the data rates to 1.39 GB/s.
That’s assuming the card can actually sustain ~250MB/s write speed during the full 1TB copy. It probably can if the card is freshly formatted but I haven’t actually tested it myself.