Entering hibernate mode after delay upon going to sleep mode doesn't work when using power supply
Oh maybe you should also set autopoweroffdelay to 60.

According to Apple's KB (https://support.apple.com/en-us/HT201635), it said: "OS X Mountain Lion v10.8.2 supplemental update 2.0 introduced a feature that lets your Mac enter safe sleep after four hours of being connected to AC power."

So it's clear now:

"standby" only takes effect when the computer using BATTERY. 

"autopoweroff" only takes effect when the computer is CONNECTED TO AC POWER.

So you should also use this command:

sudo pmset -a autopoweroffdelay 60


It should work now, hope this helps you.