1. The way roll/crawl clips work in PPro is that they automatically adjust to the duration of the clip in the timeline. An importer sets imImportInfoRec.canDoContinuousTime = true. Then in imImportImage, when it is asked to provide a frame, the importer checks the imImportImageRec.pos, which should give the time position in between the start and end of the roll/crawl from in to out (0 to 1000).
So generally for a roll/crawl, the import doesn’t know the exact in/out points in the timeline, but rather the time position between the start and end of the roll/crawl.
2. These selectors added in the past when real-time hardware manufacturers would supply a player plug-in along with their importers. The built-in player in Premiere Pro does not use imGetRollCrawlInfo / imRollCrawlRenderPage, so these selectors are not going to be called if you are just developing an importer.
3. As mentioned above, to do duration setting without a limit, you'll want to set imImportInfoRec.canDoContinuousTime = true.