I hope not more than 20~25km, even if the worst case scenario here is half the distance needed to receive all the rewards from Adventure Sync in a week.
Also, the order of rewards you proposed could also switch between each other, since in DPPt you had to hatch a Manaphy in order to breed it and then you'd get an egg with Phione... So who knows? Maybe we'll need to hatch one to complete the task and then get the other egg as a reward to hatch too.