I first used a Bridge/After Effects workflow with LRTimelapse but purchased Lightroom. Therefore I installed Lightroom after LRTimelapse.

When I go to develop images in Lightroom and select gradient I don't see the LRTimelapse gradient filters or radial filters. What do I need to do to 'activate' them?

Did you initialize before in LRT?
In Lightroom you then have to select the whole sequence (Ctrl-A) then go to Grid Mode (G) then Metadata-Read metadata from files.
Unlike Bridge, you have to manually load/write metadata to files when switching back and forth though the applications.

Yes, initialized in LRTimelapse and read metadata from files in Lightroom. I have the keyframes etc from LRT in Lightroom and the changes from Lightroom transfer back to LRT, etc. everything works fine and I have processed several videos but now need to use gradient filter on this sequence and they don't show up (haven't needed grad filters before).

Ah, just worked it out, I had 'Show Edit Pins' set to 'selected', switched to 'Auto' and can see the LRT grad filter dots now.