Per-day time preferences work incorrectly. An example: set Monday to process from 10:00-14:00. Leave the network times for Monday unspecified. This has the side-effect of forcing the network times for Monday to "Always".
Why does this happen? BOINC doesn't maintain separate preferences for CPU and network, they are both shoved into the same struct. It gets zeroed before use, and 0-0 means "Always". Because Monday is marked as "present", this 0-0 overrides the desired network times.
A secondary bug:
The advanced preferences dialog fails to always display the correct customised days. This can be reproduced by setting, say, a CPU time for Monday, and a network time for Thursday. Close the dialog, and the network time will have gone when you reopen the dialog. Perversely, the settings are saved correctly.