Negative values are shown for Time (hours) in a Time Series Field Data graph:
This situation can occur when the date and time entered in the calculation options and the time entered for time series data are not the same. In this case the negative values imply that data entered in the time series data have previous dates than entered in calculation options, so time is calculated as a negative value.
Once both date and start time are corrected, the graph should show the actual value for time (hrs).
How do I enter time series field data and add it to my graph?
Importing Time Series Data Using ModelBuilder [TN]