Can someone please point me to the page where there are guidelines on when to increase Duty and by how much? I get the contribution rank increase at 100 but I could not find guidelines on increasing scores. Thanks.

FFG developer Andrew Fischer goes into detail on this in episode 39 of the Order 66 Podcast.

Skip to about the 16 minute mark for discussion about Duty. Time stamps for the rest of the podcast are below.

Topic 1 Duty (16:00)
Q1 Explanation on awarding duty 16:30
Q2 chain of command within the party and within the rebellion (27:30)
Q3 Blending Obligation/Duty/Morality (32:15)
Topic 2 New Species careers and specializations (34:00)
Q4 Resistance of Bellow at engaged (35:25)
Q5 Commodore/Commander design process (37:25)
* Mechanics and solid repairs (42:30)
Q6 Spy has no Ranged (light), Infiltrator has no brawl (44:00).
Q7 Andy’s favorite species/specialization combo (48:00)
Q8 More species/specialization or cross-specialization combos (49:45)
Q9 Fusion Cutter (53:00)

Topic 3 Starships (56:15)
Q10 Chase mechanics (58:30)
Q11 Temple class freighter backstory (1:01:25)
Q13 Why only 1 silhouette 6 ships (1:02:55)
Q14 Sentinel Shuttle vs Lambda stats (1:05:15)
Q15 Tie Defender reduced speed (1:06:40)
Q16 Attempting an impossible task and heavy tractor quality (1:09:45)
Q17 No bulk is taken into account of tractors (1:11:30)
Q18 A-Wing strain threshold (1:13:20)

Topic 4 The Force (1:15:45)
Q19 Force rating accessibility (1:15:50)
Q20 Going from Age of Rebellion and Force and Destiny (1:18:15)

Thanks a bunch. Strange it's not in the book.