piSignage does not have a hardware clock. The Raspberry Pi time is set using NTP (Network time protocol).
So when you power off and then power on the player back, if there is no network connection , the time on raspberry pi will be set to the time pi was switched off.Say you power off the player at 8AM and turn it ON back at 10AM , if the player is connected to the internet the time on player will be accurately set to 10AM via NTP. But for some reason if the network connection is absent when you power on player , the time on the player will be 8AM , ie the last recorded time before power off and there will be a lag of 2 hours.
Now this creates a problem sometime as piSignage player stores the contents, schedule information and other settings locally and runs referring the local clock . Now if there is a lag in the player clock , the playlists also will operate with the same time lag.
Now some of our customers are using a small battery powered clock with pisignage player to avoid such situations. But as long as you are able to reconnect the players to tha network, There should be no issue.