Hi Kaonashi,
Thanks for the thorough description. The times and amounts do sound about right. With filament changes, printing times increase quite a bit due to the length of each changing process. There are some threads here in the forum you may want to have a look at. On colour change speed up and finding something useful for the waste to be used on. In particular minimizing the length of the filament path through the PTFE’s helped. But it still takes time…
I myself have never been able to properly use the “Support for PLA” filament. However, once I finally discovered and tried the usability of PETG for PLA and vice versa, I have never looked back. It works like a dream with concentric interfaces and 0mm z-separation.
Both @JonRaymond and @lion7718 made some very good points. You are already cutting down on print time by using PLA for the support but you do not need to set that separately.
For me personally, an 8h print is a prefect duration (once I am confident it works) due to relativity.
Starting around bed time means that for me, it is a relatively short print 
Best wishes and happy printing,
Eno