Not quite.
Segment overload happens whenever there's some shared media involved, such as Cable (Coax) Internet.
DSL on the other hand is
not a shared media (and fiber isn't anyway).
If you suffer from reduced bandwidth at evening hours and have a Cable (Coax) Internet connection, then most likely you suffer from segmentation overload and in that case, it won't help you to have a higher artificial capped level because your segment doesn't even offer your current one anymore.
In contrast, if you have DSL or fiber connection and the speed drops during peak times, then it's because your ISP excessively overbooked the available network bandwidth in total.
All ISPs overbook their lines, some more, some less.
In such situations, it depends on the load balancing strategy of your ISP whether he'll just cap everyone to the same max. speed, or whether you get a certain percentage of what has been promised to you.
Mike