SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '517ad4fe598d4dbc235d8e47943e2af77acada900966f87427171a026b823d17' 
  AND token = 'qRs8JJ+wwezvNAlXV79E70xgd+RfJbE70kVZ9kKrAr8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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