Q: Time Machine backups delayed

Since purchasing a new Time Capsule and updating to Mavericks from SL about three weeks ago, I've had an issue with Time Machine scheduled backups. Before setting up the TC I backed up to an external drive connected to my imac via USB. Now I use the TC for TM backups and as a router. The TC is connected to a Netgear router running in modem mode. My imac where I'm having the below TM issue, as well my ipad and iphone connect to the TC over wifi (for internet and TM backups).

Hourly TM backups start with a delay but there is no error or warning message to say there is a delay. I've read Pondini's FAQ and trouble shooting but cannot find this exact issue anywhere. I've done a full TM reset as per Pondini trouble shooting A4, as well as verifying backups as per A5, and also powering off and rebooting everything as per C19 (including hard reset of TC). None of this has changed anything.

Pondini says TM backups are scheduled to start exactly one hour after the start of the previous backup. But my backups start several minutes after the completion time of the previous backup (anything between 2 minutes and 25 minutes so far). Each time the scheduled time for the next backup passes without it starting and as a result the TM preferences start displaying the next scheduled backup an hour later (as if it just skipped one). But then the backup will start some time after the completion time of the last backup.

I will illustrate in an example with screenshots:

1. At 20:04, the next backup is scheduled for 20:05

2. At 20:06, the backup hasn't started so TM acts as if it has been skipped and shows next backup at 21.05

3. But then at 20:24, the backup unexpectedly starts. As mentioned above, then timing is somewhat random in that in can be after 2 minutes or 20 or more. The only consistency is that it always starts after the completion time of the last backup.

4. The backup has finished, it seems everything is fine (although I can't be sure). The completion time of the last backup is correct, and the next backup is scheduled for 1 hour after the last one started. But guess what... the wholem thing repeats itself again.

This issue makes me uneasy about the reliability of TM backups. I am also experiencing another issue with my TC which is linked to Airport Utility intermittenly showing "device not found". See my ongoing discussion about this issue here: https://discussions.apple.com/message/24339064?ac_cid=op123456#24339064

I have no idea whether these issues are related. Please note that the above issue with delayed TM backups is independent of the "device not found" issue i.e. the delays occur whether or not the TC is visible in Airport Utility. (When it is not visible/greyed out, both my wifi internet connection and TM backups still run).

Grateful for your advice! Thanks.