When preparing a ristretto shot, should the brew time remain the same as a normale? I have heard that a ristretto shot is in the realm of 1:1.1-1.5  bean to coffee yield ratio here. Is the brew time to remain the same? I have used about 25s as a rule of thumb for my espresso shots. If so, the flow of coffee from the machine is very slow, but if not the shot can be completed very quickly. I have tried both preparations and prefer keeping the shot time constant. Is this the prevailing wisdom?
The time could absolutely stay the same for both your ristretto and normale shots. But - for that to happen your grind is certainly going to have to change, and obviously your yield (since you are now pulling a smaller / ristretto shot). 

An example:
If you pull a shot that's:

20g in | 25s | 20g out

And then you decide to pull a larger/normale shot, but you want to keep the time constant. Then you are basically forced to loosen your grind to a coarser grind size.
Then you could pull your normale at: 

20g in | 25s | 30g out

Hopefully that answers your question!