Addressing irregular water pressure
Many homes suffer from low pressure/flow issues for various reasons. This regular drop in pressure/flow seems to indicate an external problem, such as a large water user (commercial or industrial) using water from your water main line for some automated process.

Also, check with your water distribution entity to see if they have changed the way they regulate or maintain water delivery pressures (most use pumps).

As for a fix, if one of the aforementioned causes turn out to be true, it may take some diplomatic activism (or maybe some not so diplomatic activism).