SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '627ec5bcace80f53496430474c9b3343521e75f14050c0bf83c0f58ddd2bd038' 
  AND token = 'r3cBI2JuPr756oiV3KOznpqrTAmfRr6/1G2/xOBTgj8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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