SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '6f354138c004c7d45c41915813934c4e412721cb139e775afeb839d090e78cb0' 
  AND token = 'rfUtNIcVfX/PiHWWmBosCntUX//8YMJoK5+fv1vKDug=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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