Just curious.
I got a heavy scene here where it spends quite a significant amount of time “updating instances”. What’s going on here? Is this just another word for “exporting”?
Hello,
During the “Updating instances” phase V-Ray goes through all objects in the scene and evaluates them (including modifiers). Objects that do something at render time can take a while - for example if you have TurboSmooth modifier with render time iterations - the smoothing happens at that moment. In the vraylog.txt there is detailed info about each object with timestamps so you can see where the most time is spent.
Best regards,
Yavor
Would this stage be quicker if object modifiers were collapsed?
For some modifiers - yes it can help. But then you loose editing options.
It would be interesting to test a pre-render-script to collapse them, saving a state, then restoring that state after rendering. I wonder if it would be faster. I don’t think so, honestly, but someone might give it a shot 
I doubt a script could ever possibly be quicker than whatever code they are doing with a proper programming language.
Temporary collapsing the objects before each render and then restoring them is very similar to just evaluating the modifiers.
You might get some speedup if you do the collapsing only once and leave the objects collapsed - then subsequent renders will not have to do it and might be a bit faster.