SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b789abb3ab76c42512b3b4da6e71fce194041f16b5f360b4b650370b1835b655' 
  AND token = 'eLp10cD8nTcoDPNczW7UFnbT6RGuXUoewLujVwXMLN8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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