At what date and time UTC is JWST's unfolding of its sunshield scheduled to begin?
At what date and time UTC is confirmation of success expected if all goes smoothly?
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(Partial answer, as a complete answer would include the nominal mission timeline.)
The unfolding of the sunshield is scheduled to start on the third day of the mission. From this page:
Forward Sunshield Pallet
This step begins the Sunshield deployment phase.
Nominal Event Time: Launch + 3 days
The deployments team begins planning and operations to deploy the forward Unitized Pallet structure (UPS). The UPS supports and carries the five sunshield membranes. Prior to this, the spacecraft is maneuvered to provide warmer temperatures on the forward UPS and various heaters are activated to warm key deployment components. Key release devices are activated. Various electronics and software are configured prior to support the UPS motions, which are driven by a motor. This represents the start of all major deployments.
This NASA blog post provides the same information as the aforementioned NASA page, but in a handy list format. It also mentions that:
The process involves hundreds of individual deployments. It is not an automatic, hands-off sequence; it is human-controlled. This means that the order, location, timing, and duration of deployments may change.
The launch was on 25 December 2021, 12:20 UTC, so in theory the deployment phase can be expected to start on 28 December 2021, around noon UTC. The above quote implies quite some manual tasks involved, which can explain why it is difficult to find a more precise timeline (i.e. at the hour level rather than than day level).
Sunshield tensioning is scheduled to be completed on the 8th day of the mission, so around the 2nd of January, 2022.