This is an unofficial update to @aTo's Mount Feed Timer that fixes it for the v5 update. It will be removed if @aTo uploads an official version. From the addon's page:

A simple AddOn to show the remaining time before feeding the active mount.

New Feature:
- Now all mount is tracked but only the smallest timer is displayed !
- Lock / Unlock window
- Display when (Always / Hide in menus/ Menu only / Timer < 1 hour / Toggle keybind)
- Title choice (Feed timer or Mount name)
- Timer format (hh:mm:ss or hh:mm)
- Text size
- Text font
- Text style
- Manual or auto text color