MacOS – How long before Standby/Deep sleep mode is activated

SleepWatcher works fine with Mountain Lion. I've written an extensive guide to address the exact problem to unmount and auto re-mount of SD Cards and any external HDDs using sleepwatcher.

To disable deep sleep, run the following command in Terminal:

sudo pmset -a standby 0

This is a description of "standby" (deep sleep) from the pmset man page:

 standby causes kernel power management to automatically hibernate a
 machine after it has slept for a specified time period. This saves power
 while asleep. This setting defaults to ON for supported hardware. The
 setting standby will be visible in pmset -g if the feature is supported
 on this machine.

 standby only works if hibernation is turned on to hibernatemode 3 or 25.

 standbydelay specifies the delay, in seconds, before writing the hiberna-
 tion image to disk and powering off memory for Standby.

Battery savings depend on how much time your Mac spends in standby. While in standby mode, your Mac consumes 0 power, it's as if it is shut down (note: not taking Power Nap into consideration).

My personal recommendation would be to set the "standbydelay" value to something bigger. 2 hours, for example. This means that if you open the lid back in less than 2 hours, your Mac would be in regular sleep and wake up instantly. If longer than 2 hours, your Mac would enter standby mode and consume no power, and waking up will take a bit longer.

Example for 2 hours:

sudo pmset -a standbydelay 7200