How to properly use count_over_time

Can someone help me understand how to query for different specific time ranges in Grafana? I’m using count_over_time, and I want to subtract the count of systems that sent the line “Timestamp” in the last hour from the count of systems that sent the line “Timestamp” in the last minute. Both outcomes seem to depend solely on the dashboard time ranges, not on the values I input. Am I using the functions incorrectly?

My end goal is to visualize this number in a pie chart. So, if transformations might help here, that would also be a viable solution.

Timestamp sent in the last hour:

“Supposed to be” Timestamp sent in the last minute:

Adding these number up should be 1 not 0: