[bug 1050766] Measure delta between creating a task and it starting

I think this will work...

r?
You want `lag.total_seconds()` because "seconds" here is the seconds < 1 day. So if we had problems like last week where tasks would take 4 days to get through the queue, we'd have a totally wrong number here.

Also, we're dealing with servers that might not be totally in sync time-wise. My vote is we at least change it so that we're gauging minutes--not seconds. i.e. divide by 60.

Also, the server times could be such that we end up with a negative number here. Maybe it's sufficient to have a floor of 0?