I had the same problem, but I guess it starts when flashing TWRP on a device that has not the right date/time set before flashing TWRP. (I was too eager to change ROM on my device, so I never bothered to set time/date on the device's initial system before flashing TWRP - That's why many other users do not have any problem at all with time/date of TWRP, they simply used their device already with the right time set before flashing TWRP).
So after flashing TWRP I noticed that the time was wrong (and when making a backup I saw that even the date was wrong). It showed that it was the 1st January of 2014 (default date when not seting date on this specific device).
So, after some time I found out, that you have to FISRT SET TIME/DATE on your device's system and THEN flash TWRP. TWRP will then get the (right) time/date of the system on your device.
Another thing that was interesting though, is that TWRP's wrong date/time would even show in the system of the device, if the device was set to get time/date from the network but couldn't connect to it.
So it seems that TWRP get's its time/date setting from the device's system when it's initially flashed, but then the system of the device takes the date/time from TWRP, as it is like a layer "before" the system.
So to cut things short, if you have TWRP flashed and it shows wrong time, try flashing another recovery (CWM) or a stock ROM (over Odin), set the right time on your device and then finally flash TWRP again. (TWRP is much smoother than CWM in my opinion and worth the hussle).
All the above were executed on a Galaxy S5 SM-900F and by system I mean the android version installed on the device.
Good luck!