SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51ec59a3ba8b3f6272e6be09c17e3ff0cce255984e81bd1c4aa4e48176250a5d' 
  AND token = '3Bp4fEBQbVW4WasdOaTqVAeQBgdLEiTTBnUx5kPoPzk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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