By HDL protocol there is no temperature parameter assigned to "Timer" mode. You can just select it to activate timer but there is no desired temperature for the mode.

I think we just have to block the temperature control in Timer mode. If the idea will be approved we will make the change in the module.

Do your FH module have the "Timer" mode set? Can select the mode with panel?
If no - you can disable the mode in module settings. If you do have the mode set we will find why the mode is not working

Which platform do you use?
Do you have last version of i3 lite app?
Which version of FH module do you have? (you can see it in i3 lite app in the "Module information" section)