Just keep doing it. There's no time limit, do a book each time you play. Honestly once you get past those books it's easier.

If you need a specific fate to pop - just do the other fates on the map. There's a limit to how many spawn, so you'll spawn if quicker by getting rid of the ones already there. No point standing around waiting for it to pop.

I've done the Dragoon one myself, I'd never do another one I don't think. Unless I had absolutely nothing to do in-game anymore