"lose track of time" or "lose track of the time" mean that we don't realise how late it is, usually because we are very busy, or distracted with something else.

Thanks a million dear Dave.

When you lose track of something, you become uninformed or unaware of it. So when you lose track of the time it means you were unaware of the time, usually meaning you're late for something. I was so busy getting ready for work I lost track of the time and missed my bus.