I’m not sure about the new “SmartThings (Samsung Connect)” app, which has a different rules engine, but in SmartThings Classic you do get some stacked conditionals through the “more options” at the end of the automation setup screens.
Official knowledgebase article:
As you were configuring this simple automation, you may have noticed other, more advanced options. Smart Lights lets you add several restrictions and parameters to totally customize your lighting automations.
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If you’re ready for the next level of automation, keep reading to learn how to:
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Turn on the hallway light when you arrive home, but only between 5:00 and 10:00 PM on Saturday when the Mode is set to Away.
It’s not easily discoverable, but it is there. As others have mentioned, the biggest advantage to the official smarts lights feature is that at present, it’s just about the only thing that can run locally. Everything else runs in the cloud, including CoRE and webCore.
(Timeout for a terminology note…in a SmartThings context, “Core” refers to a specific custom rules engine built by the community to add functionality missing in the official features. This later evolved into WebCore. So anything you read in this forum about “Core features” is pretty much the opposite meaning as “something provided in the official app.” So “Core can do that” means “The official features don’t do that, but the custom rules engine built by the community can.”
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Anyway, start by checking out the advanced options at the end of the official features and see if they fit the specific use case you are trying to automate. If it’s just a matter of adding day/time or Mode restrictions, they probably will.
If they don’t work for your desired rule, you can move on to WebCore. 