I got the follow excerpt in my inbox today from NPS staff:

Soon we'll have to do a temporary closure at the base of the ramp leading from Rosslyn. The exact date of the temporary closures unknown at this time, but could happen as soon as tomorrow. This temporary closure will allow us to pave that section. While the date is unknown we're planning to do the work outside of peak times (rush hours). The work will start at 10 am and will be completed before 2 pm. It will only be one day.

The contractor is required to have a flagger on the ramp to notify trail users.
Followed up by:

The work will happen sometime between tomorrow and COB next Friday.
Further details will be posted as they develop...all appropriate questions have been asked to hopefully clarify details.