There is no normal time with GI renders.  It will vary greatly depending on what content is in the scene and how it is lit, and how render settings are configured.  The only safe bet is that it will always be significantly longer with Indirect Lighting/GI than without. Particularly when people don't really know what their content is - how many polygons, how it's modeled, how their lighting works (canned light sets) what materials settings are applied, or how their render settings are really set (canned render settings), there is just no way a lot of people will have the faintest idea of how long a render is going to take until they actually run it.

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