If your bodyguard is currently at 130-51 hp, it degrades 1 hp every 24 hours.
If your bodyguard is currently at 50-36 hp, it degrades 1 hp every 48 hours.
If your bodyguard is currently at 35-2 hp, it degrades 1 hp every 72 hours.


In summary, if your BG is at low HP, it degrades at a much slower rate than those that are at a higher HP.