Convert SMTP uptime to days?

The SNMP_Host_Uptime datasource has Uptime datapoint that displays uptime in seconds. 

You can check ‘perform an expression on datapoint’ in the table widget column settings to convert the value from seconds to days by dividing the uptime in seconds by 86400, this would display the Uptime value in days in the table widget.

https://www.logicmonitor.com/support/dashboards-and-widgets/widgets/table-widget#:~:text=2%20Decimal%20places.-,Perform%20expression%20on%20datapoint,-Embed%20a%20groovy 

Alternatively, you can create a complex datapoint that converts the Uptime from seconds to days using the same equation.

https://www.logicmonitor.com/support/logicmodules/datasources/datapoints/complex-datapoints