When syncing my iPhone with iCloud, it only takes a few seconds (a few minutes the first time I synced). However, when I went to create a full backup through iCloud, it first said 29 hours of time remaining. After about three hours, it said 23 hours remaining. Knowing I need to be somewhere tomorrow morning, I tapped the Cancel button. Then I attached my iPhone to my computer and created a full backup in about 5 minutes. The first attached image below is the screen for syncing. The second attached image is for full iPhone backup. The third image below shows the "29 hours."