Reduce the default task start delay from 5s to 3s
Reduce the default task start delay from 5s to 3s

Summary:
We tried this before, there were failures, but they weren't clearly attributable to
this change, and we don't have a working theory on why this would cause issues, so
let's give it another go.

Test Plan: Prod, I guess.

Reviewers: paulruan

Reviewed By: paulruan

Subscribers: changesbot, alexmv

Differential Revision: https://tails.corp.dropbox.com/D165589

dropbox/changes,dropbox/changes,dropbox/changes,dropbox/changes