date and time are controlled by and set by two factors.
1. The BIOS in the intitial set up.You can check this by pressing delete whilst in the 1st start up screen [POST]
2. Operating system to the local time as set by you
Both of there are controlled by a small watch type bettery on the MoBo,
The most common complaint is losing time most often cause by the gradual battery run down [typical life 3 years] Easy to replace sold in all places that sell watch type batteries.[Boots is a good place]
The fluctuating time mentioned by you is a mystery
at the moemnt daresya more will come to light.