I have heard 10 to 15 minutes as being common.
These same users don't complain about using a key on the door to get in and out during non banking hours. If they did, it wouldn't change the fact that you lock the doors. The same applies here. Any time you want the screen data protected from eyes without a need to know, this is a safety precaution. While you may compromise by giving them a few more minutes, based on their location, they need to understand why this is in place.
More than once I have seen a banker in a glass lobby have their back to the glass and those pedestrians outside can see the employees monitor. When it gets dark outside earlier, as it does now, they are that much easier to read.
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AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell