Premiere does not adjust the duration of the clip automaticly.
Easiest way to me is to render out the slomo and import that into Premiere.
What is the best way to render out the slow motion and then import that into PPro? Also, how do you select the best quality frame blending since that box is not available on a linked composition?
If its not available then copy paste into AE instead of DL.
Export as uncompressed.
Actually, you don't have to render your composition out of AE so as to get proper duration of the dynamically linked comp in PrPro. As Ann said, PrPro doesn't automatically expand dynamicalli linked comp in the timeline but perceives it previous duration as a cut. Therefore, in addition to dragging it to the timeline from Project panel or increasing duration you can just pull its tail in the timeline.
Fuzzy and Ann are correct in my opinion. Premiere Pro thinks that the duration on the timeline is just the first part of a clip that has been given a rather long handle, so to speak.
Just drag it out as far as it goes. Premiere Pro will not let you drag it out farther than the end of the comp under these particular circumstances.
Why not do that automagically for you? Too dangerous. What would it do with anything on the sequence out to the right of the clip? Overwrite it or push it?
Now, I suppose that a good way to do that would be to alert you about the problem when you return to Premiere Pro and ask you how you want it handled, but that would take a Feature Request. And I am not sure what would need to happen if you had made a bunch of changes to other links other than that one before returning to Premiere Pro.
Before I suggest that you do that, I have to ask why you didn't just use the Time Remapping feature of Premiere Pro do do the same job. That way Premiere Pro would have known what you wanted to do. I understand that Timewarp and Time Remapping both have different strong and weak points, I am just curious if you tested both and decided on using After Effects for a particular reason.