SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '281c42692e482978037693f5c48c29202e12b0fe163a5b464aa201f026f15537' 
  AND token = 'B/qsU+c+vQLki8hw3bPf41jfO7JET/ROFw3YPvERuJM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}