I am making a single 24 hour time-lapse and combining the best footage from several days, in some cases out of temporal order, but still in visual order - i.e. midnight to sunrise to sunset to midnight. Ah, the "cheating" we can do :-) 

So - in Lightroom I have made a Collection so I can manually order the images to be in visual sequence, since sort by capture time will not work. How do I import this into LRT, which seems to only be able to see folders? 

So far the only workaround I can think of is to rename the files in LR, imposing a new numerical sequence, then moving those to a new folder. However I prefer not to lose the original file names as they help for error checking when combining various folders.

Just set Lightroom to rename the exported files (make your own Export template that matches the LRTimelapse naming scheme LRT_xxxxx.jpg)

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Thank you Gunther. I just did the rename in LR without exporting, as that takes a few minutes instead of a few hours (for thousands of images) and doesn't use any more disk space. 

This works fine and the time and storage savings seems to be worth the inconvenience of losing the original filenames.

A bit confusing to me - since normally you would have to export anyway from Lightroom, after you did the editing in LRT/LR.

I meant I was saving doing two exports, one just to rename files to get them into non-temporal order. I start all work in LR, importing photos, organizing sub-sequences, re-arranging order, editing photos to see which parts can be blended to hide edits, etc. When I'm finished that I need to rename the files to set the sequence order. Then I import into LRT and work as usual, and at the end I do export from LR.