SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50746893a4de412490460fca87762bd267465577a00713d8858d2ac751cdf31b' 
  AND token = 'cJUQK+J1ulZagt8IyaYkh9RMhOhwzXwLcRptBZcbeRY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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