On Windows 11, the correct syntax is:
curl -X POST "http://localhost:1000/Schedule/0" -H "accept: */*" -H "Content-Type: application/json" -d "{ \"title\": \"string\", \"timeStart\": \"21:00:00\", \"timeEnd\": \"22:00:00\" }"
only 1 backslash before each double quote inside --data