You get 20 diamonds from dungeons Monday-Saturday, and 4 from shard combos (400 shards) for a total of 144/wk. Gem Bounties on these days also give 20 diamonds and 4 from shard combos, for a total of 144/wk. Sunday gives 74 daily from dungeons (20/20/30 diamonds, 100/100/200 shards or 70 diamonds, 400 shards) 84 for the gem bounties (80 diamonds, 400 shards). Tasks give 25x6 Diamonds (150) and 3000 shards (30) or 180 diamonds. So 144 + 144 + 74 + 84 + 180. Grand total, 626 Diamonds per week with all gem bounties (about 6.4 weeks per cycle), with no Gem Bounties except Sunday being 482 per week (about 8.3 weeks per cycle).
An 8 week cycle vs a 10 one would mean about 500 diamonds per week versus 400 diamonds per week. You can get those numbers exactly if you both ignore shard conversions and only assume five days for “weekday” packs instead of six as they are Monday-Saturday. Then, you’d have 100 weekly diamonds for the “weekday” dungeons and bounties, 70 from the Sunday dungeon, 80 from the Sunday Bounty, and 150 fro the guild tasks. (100 + 100 + 70 + 80 + 150 = 500).