This is only if you want to do this right away if you are doing everything you come across. You can get this out of the way in Chapter 5 just after acquiring Ramuh. On your way to the final objective you want to make camp at Lingagh Haven (Near the road in Rydnelle Ley). After camping, make you way to the road and look for these 'little' fellas in the video.
They have a lot of hit points so its easy to just use the auto-attack to drag out the fight so the summon prompt appears - I was around lvl 45 due to side-quest OCD, so I was a tad bit overlevled at this point. You will need to HOLD DOWN the trigger for a few seconds before the summon actually starts. Once it happens you'll get the satisfaction of seeing prior to the scripted event.
Video taken from my PS4 copy: