Quest Stages 8 and 9 are a bit unbalanced when taken together, particularly for cities that are just starting a new age. The problem is in the part that wants you to "Delete 7 units from your age or spend 15 forge points", then "Recruit 5 units from your age or 6 from the previous age". Here are my four cities as an example:
* City 1: mid-Early Middle Ages. Most of the military options are in the mid-to-late age, and I've been focussing on other things, so I don't have 7 units in my age! I've had enough warning, though, so I've built a second Mounted Archer Range, and will likely get through Stage 8 in a few hours when I get there (won't quite have time to build 7 units, but it should just be one unit to build for each building when I get to that stage). For Stage 9, I'll want to go with previous-aged units, though, which means I'll have to delete another 6 units from that age to make room, then spend about 2 hours apiece across three military buildings, so 4 hours.
Approx time to delete/recruit units: 8 hours, 13 units deleted.
* City 2: earlyish-Early Middle Ages. Already at Stage 8, but I hadn't clued into the problem before I got here. I deleted the 4 units I had from that age, and started on a second Mounted Archer Range, but it's still going to be a while before I get the full 7 units deleted. If I hadn't had room for the extra building, it could've been up to 12 hours, which would've made FP the better option, but with the second range, it'll only be about 7 hours, I think, between construction and training. Same problem with the unit reconstruction as above.
Approx time to delete/recruit units: 11 hours, 13 units deleted.
* City 3: very early-Early Middle Ages. I have absolutely no military units of my age yet, nor am I anywhere close to researching and building a Mounted Archer Range. I have no choice but to spend the 15 FP. That's 15 hours (give or take random FP rewards) for Stage 8, plus another 4 hours (counting only the recruiting) for Stage 9.
Approx time to delete/recruit units: 19 hours, 6 units deleted.
* City 4: late-Iron Age. 7 units will be deleted instantly, and among five military buildings, Stage 9 will be completed fairly quickly.
Approx time to delete/recruit units: 2 hours, 7 units deleted.
I think Stage 8, like Stage 9, should've been "Delete 7 units from your age or X from the previous age". This would've made these two quest stages complement one another and be much more uniform across all ages and players.