Why does Sleep Mode increase my SSD's Power On Hours SMART stats?

[macpokerstars]

When I put my Macbook Pro in sleep mode, it never increases the "Power On Hours" SMART stats of its SSD.

However, when my iMac 5k Late 2015 with Sierra is put to Sleep, the Power On Hours have increased by 8 units in the morning.

Why is that happening?

When I put my iMac to sleep at 3:28am, here is what I get in the log on afterwards:

2017-04-17 05:28:54.625624+0100 localhost kernel[0]: (AppleACPIPlatform) Wake reason: EC.SleepTimer XHC1 (SleepTimer)
2017-04-17 05:28:54.625625+0100 localhost kernel[0]: (AppleACPIPlatform) Wake reason: EC.SleepTimer XHC1 (SleepTimer)
2017-04-17 06:29:35.964576+0100 localhost kernel[0]: (AppleACPIPlatform) Wake reason: XHC1
2017-04-17 06:29:35.964577+0100 localhost kernel[0]: (AppleACPIPlatform) Wake reason: XHC1
2017-04-17 08:30:33.853540+0100 localhost kernel[0]: (AppleACPIPlatform) Wake reason: XHC1
2017-04-17 08:30:33.853541+0100 localhost kernel[0]: (AppleACPIPlatform) Wake reason: XHC1