Garry Kilworth's story "On the Watchtower at Plataea" involves a group of time travelers, from the story's "present", who push back earlier and earlier into the past... until they can't go any further because another group is coming the other way, from the past (due to the technology involved, each prevents the other from going further in their desired direction).

The "present" group then end up, essentially, in a standoff, watching the other group from a vantage point near an ancient Greek battlefield, and pointing out that they must eventually "lose" because both groups are now essentially in normal time. Which is moving from the past to the "present" from which they left.