Your problem is likely with the grinder rather than the espresso machine. You almost always have to dial in again after the morning rush as the burrs heat up and expand, then cool back down as things calm down a bit. Ambient temp has an affect but not as strong as grinder temp curves.

Perhaps grinders should be designed to blow air through the burrs when they aren't grinding. But in most cases, change comes very slowly in the espresso world.

I find that a flow profiling machine helps compensate for grind variations (ie, much less change in taste as grind changes with burr temperature).