HT203177 very long 'preparing for backup' for Time Machine

None of the issues discussed in the apple support page on this issue seem to apply to me (except one below regarding not completing the 'prepare for backup'). It still takes way too much time (a night is not enough) to prepare for time machine backup, even though there was a backup recently, and it is not a one-time event but a recurring problem, and there are no big changes to my files or disks.
And of course because most days it does not complete the backup before I have to leave to work, the condition on 'not interrupting the backup' cannot be respected. This looks like plain poor design.
The only thing that helps is to connect my laptop directly to the Time Machine by Ethernet but it is very inconvenient.
This is really annoying. I wish I had bought another disk back-up solution.


saggybaggy wrote:
The Mac Pro I'm backing up is Leopard 10.5.8, could this be the issue?
No, Time Machine works on 10.5.8.
I'm trying to back it up before I upgrade my operating system.
Good plan! 
Also, for the backup I'm using the same external drive that I used to backup my MacBook Pro already... not sure if this would cause any issues in preparing.
Not in preparing, but it's usually not a good idea to use the same partition on the same drive for both.  See Time Machine - Frequently Asked Question #4 for an explanation.