Consider adding task start time

[cjpatton]

When deciding whether to opt in to a task, a party knows only when the task expires, not how long the task was in use. Imagine for example a client uploads a report to a task that expires in two years; then two years minus one month later, the Leader wants to aggregate it. Should the Helper oblige?

It sounds reasonable to include in the TaskConfig an indication of when the task began.

[junyechen1996]

While working on this: Can the aggregator figure out the start time when it receives the first report of a task ID? In the example:

for example a client uploads a report to a task that expires in two years; then two years minus one month later, the Leader wants to aggregate it. Should the Helper oblige?

I think this is a valid case for helper to just process the request, since the task hasn't expired?

[cjpatton]

My suspiciion is that it will be helpful to stamp when the Task Author intends for the task to begin. That way we can reject reports with timestamps begin prior to the start of the task.