How can I get Streamstats to Calculate all Fields?

[aohls]

I am using the following search which returns a table with three rows:

    | streamstats current=f last(_time) as NewTime first(_time) as LastTask by Item
    | eval Duration=NewTime-_time
    | eval RunTime=(Duration/60)
    | table JobName, RunTime, _time

The issue I am having is that my time is only caluculated for two of the rows, the earliest two. The final record is not calculating a time so I am getting the following:

JobName,RunTime, _time
Name1, ,5:00
Name2,120,4:00
Name3,60,2:00

Is there a way I can force it to calculate the final time?

[somesoni2]

The problem is that there is no last(_time) for row appearing first in result (would be the last result if sorted by _time), hence no calculation is done. What should the RunTime value for it?