Engine.time_scale will affect everything and you can't make exceptions. You could take it into account with your
If you want more control you could define your own time scale, being
1.0 by default and scaled however you want when you need to slow or speed up time. You then use this value with
deltato control at which speed things should go. This allows you to only slow the process function of a character for example, without affecting timers or anything else.