SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a521f7939f6b92579958ac226f6aa0e3a3cec49416847183fce79ecccdf8823a' 
  AND token = '6mrAoqhxjet/tWFUwVPFzn4chJmRrlbDUTyBEuZYHY8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}