If it should be done only twice a day sleeping for 12h would be even more error prone and you would be even less likely to have it actually run at that time.
Also, if it should be done only twice a day you don’t really want it to run twice a day only since you can not guarrantee that you have internet exactly at the time when your timer expires, you would want to check some “last_updated” timestamp and check if it was more than 12h ago.