@Bruce is right. You'll need Meraki support to extend the timer for you. If you are using the newer AnyConnect client you can configure this in the client profile yourself. I'm not aware of any systems that support TXT messages. Note that TXTing of codes is not generally considered secure, especially in countries like the USA with poor TXT security standards (security costs money and Telco's in the USA don't seem interested in spending on customer security). https://www.techrepublic.com/article/top-5-reasons-not-to-use-sms-for-multi-factor-authentication/ As Bruce alludes to, you'll need to use a system that supports push notifications like Cisco Duo.
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