SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '6b645fb6624d5fd3a6848fa81eaf2846906f5500251271dccee0ced23a226497' 
  AND token = 't4UboCJBHDtJn3dsxZxRht0+AjCuRVKsy+7rqbDhQfM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00029

JSON explain

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