If you haven’t backed up with Time Machine in a while, the latest backup status will change to ‘Delayed’ and the menubar icon will have an exclamation mark in it reminding you to backup soon. Resolving the backup delay is easy to do, just pull down the Time Machine menu and select ‘Backup Now’, as long as you have the Time Machine drive attached, your backup will go as usual.
Common reasons to have the ‘Time Machine Backup Delayed’ message:
* You have manually stopped the Time Machine backup process several times
* You have detached the external device that Time Machine was backing up to
* You have recently changed the Time Machine backup drive
If you have recently changed the Time Machine device, make sure Time Machine is aware of the new disk location by checking out the Time Machine preferences within System Preferences > Time Machine. The name of the backup disk will be listed, if it’s an old drive or you want to switch it, just hit the ‘Select Disk’ button and select your new backup disk.
I recommend to just let Time Machine run on it’s regular backup schedule so you can prevent delays and keep your Mac backups as accurate and relevant as possible. You may not need them often, but when you do, you’ll be glad you have a recent Time Machine snapshot to revert back to.