He had completely lost track of time, but something made him look up.

After the first few weeks, he had lost track of time.

He had lost track of time; his days seemed to do that more often than not.

It was difficult for me to keep track of time.

After that, he found it most difficult to keep track of time.

He or she should keep track of time and let the group know when to move on to another member.

Six months, maybe seven, he had lost track of time.

Decided to take a walk and lost track of time.

How does someone without a watch keep track of time?

All these things led her to believe she had lost track of time.