P: Edit Capture Time issue - Need a way to set all photos selected to same date & time

Background

• I am scanning thousands of slides and negatives into Lightroom
• I have details of many images recorded
• I am manually applying Data/Time capture metadata to groups of images in Lightroom: the Time is unknown so I use 00:00:00

Problem

• When I make a bulk metadata adjustment to Date/Time the date is OK but the time is incremented by the time difference of the scanned image.
• I currently amend each photo individually, which is not really a practical solution

Solution sought

• I want to apply a specified Date/Time to every photo selected
• (Dealing with an unknown day or month is a different problem which I'm skipping here - I have read the forum discussions on the topic)
• Is there an appropriate plugin or external application?

Supplementary question

• I  have other metadata recorded, such as camera, lens, exposure, etc.  How do I record these in Lightroom?

Why conversations get merged:

https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-auto-import-to-folders-organized-by-date/5f5f44f14b561a3d422ab0ba?commentId=5f5f48984b561a3d422bdf45 

As a workaround, see the Capture Time To Exif plugin.

There are many external to Adobe photo programs that many of us use to share photos.  Most all of them would benefit from this batch date idea.  My 37 grandkids cannot afford to all buy and learn LR.  I do that for them then export to share.

I like this but for a different reason. I use Google Albums for sharing my photos and Google sorts buy one of the dates in the images (not sure which one). So I'd like this option as well or if someone can suggest a separate program for batch changing these dates to a starting data plus time increment. 

Sorting by "date taken" is the most common sort sequence for most viewing programs.  LR Metadata - edit Capture time uses something of a relative change process that often ends up with wild unmeaningful dates.  That works great to sync various camera's used during a single shoot.  But for scanned pics, or many other intermediate sources of pics (like Shutterfly) that date is changed to the "date captured"  (date processed by that scanner or intermediate program).  Example, to merge a number of pics from an event like a family birthday or wedding taken by multiple family members.  I know the real date and want a way to force the date that I specify to change uniformly as I enter it across the entire batch.  I may want to set the correct date first, then guess at the relative time to make the sequence seem logical.  (Walk down the aisle comes before the I do and kiss).  Having pics from one good modern camera is a big aid as a master source, but for many family event pics received from multiple sources, all you have are the date a scans of old prints was made, or the date accepted into an intermediate system like Shutterfly.  I have had ten plus different dates for the same event, some years apart.  Let me force the date to what I know to be valid for an entire selected batch.

Perhaps two selection buttons - "Relative Change" and "Specified Change."

As a workaround, see the Capture Time To Exif plugin.

Why conversations get merged:

https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-auto-import-to-folders-organized-by-date/5f5f44f14b561a3d422ab0ba?commentId=5f5f48984b561a3d422bdf45 

Another factor that might be affecting your experience concerns whether you selected the set of files from the grid view or from the filmstrip. If they are selected from the filmstrip, only one of them will  be affected - and that seems to be true for all kinds of actions, such as pasting settings.