SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21e6eb2cf05544cc89d36067032218bf83c8ce4e44c736820163c23add5e8ace' 
  AND token = 'WC9DbjSssycfHrcLl22224lLpB86RjgpY/ybPK2pVGc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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