SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '55d9edb83c8a371a941569e427514591730f79613b42d63feb86e67db437f356' 
  AND token = 'QPHo34x1qabdANWzExTUVdPGGRf8q8o8o4Wc/7rWnoQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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