SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8503ff4d48659a55e76aba286fc355f3ea95f6ad03b8a67235582746daec450c' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00030

JSON explain

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