SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6e423dfc8dc030045854a927b451fe1e1218304248c3e01c693adff8d31c7239' 
  AND token = '6cFVeCuRjke5s6U1UkeAo/xBqDplGUlyusErt9cu7c8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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