fixes for time spent pilot

[cforkish]

this includes a few fixes to the functionality for the time spent pilot

1. main issue: we were parsing timestamp values of seconds as milliseconds, resulting in the wrong displayed date
2. modifying a section in the "manage students" tab was resetting our section progress redux, so we were losing the flag for the pilot
3. expanding rows PR regressed table header border widths
4. update to round time spent values up instead of down, to avoid lots of 0's

Links

• jira ticket: LP-1845

[cforkish]

this change is unrelated to the PR task, but included as a general QOL improvement. when i went to track the redux flow that was resetting our pilot flag, i had trouble finding usages of this component due to a typo in its name.