Seems reasonable. I'd verify by doing something like this, and checking for reasonableness and number of events ...
host=MyHost sourcetype="Perfmon:Network Interface"
| eval MB_Usage=10*Value/1024/1024
You could also do this...
earliest=-1d host=MyHost sourcetype="Perfmon:Network Interface"
| eval MB_Usage=3600*Value/1024/1024
| timechart span=1h avg(MB_Usage)
If the value number is per second, then 3600 times that value number is the data per hour at that moment, and the average of those will approximate the total amount that particular hour.