Not extremely difficult of a mission (for Eastern Realms standards). The Fallen Angels are pretty deadly but just aggressively focusing the lairs and resurrecting your dead heroes will work pretty well.

I initially tried to beat the Timewalker (which no hero will try to kill) by building a string of Wizard Towers to it and just blasting it with lightning, but it just wasn't enough damage and it was just getting stronger by the day.

Eventually I was like "I bet my heroes would fight it if it just randomly showed up", so I closed my Fairgrounds and then cast Dismiss on the Timewalker, which put it just in the edge of my settlement. I then spammed Vines as my heroes swarmed it. Took a while but they eventually burned down its health.

Done in 36 days w/ Krolm. Heroes aren't interested in going after Time Walker even with 5k bounty unless they are already quite close, so had to use Dismiss to shift it to the other side of my base and then trap it on it's way back with Wizard towers and surrounding heroes. I'd rank this Quest as Expert, not Master (Chapter 3 ironically is listed as Expert but is definitely Master!)

I had the same tax collector bug that SilverDragon reported - all my tax collectors just stayed inside (guardhouse, palace, outpost) and weren't collecting. I was able to use the rogue guild's extort to get it, but it was very heartbreaking to see my marketplace with 60k gold and my tax collectors just on vacation. I was using no other mods.

Had a weird situation where despite putting down 35k bounty on the the Timewalker (I had 100,000+ gold), I couldn't get any of my heroes to bite. I eventually spammed about 50 ballista towers in a ring around the walker, and once he finally waded into my trap I was able to slowly whittle him down (he had 1200 hp), using the paralyze spell to help. Granted, I was using New Game+, so this might have messed with the heroes' loyalty to bounty flags.

Cool idea, but this mission is really easy. After some time the Lurker stops pressuring you with summon portals. Basically you want to clear out the map out of dens, get many heroes, get Temple of Dauros lvl 3 to disable this guy infinitely while your heroes kill him. Though, you need a lot of money to spam the spell. I did around 50% of damage via Lightning spell, but I waited out for too much because he had something around 4k hp.
One issue is that no matter how much the bounty on this guy was my heroes refused to attack him, so I had to place explore reward near him so exploring heroes would start fighting him.
I'd say the guy needs to scale up a bit more and not just in HP, because no matter how much HP he will get you still can do insane things in terms of economy with the spare time after attacks.

@precious pearl - Sorry but that is due to those mods you are using, this quest isn't compatible with other mods.

bug: https://prnt.sc/u3ulgw
i'm using majestic majesty and maybe another mod, and something's causing it to spawn these werewolf fighters like every half-second, flooding the map.. lol

Bug: After I think 30 days or so...my tax collectors stopped collecting. They just stayed in the palace. I had 3 market places and one of them had over 40k gold that hadn't been collected. Luckily I had a rogue's guild built so I could extort otherwise that could have ended the game for me. Other than that it was a fun quest. Didn't find it to be "master" difficulty though.

Second time doing it, thinking slightly outside the box trying to get it done faster..., day 2 win is possible! (hint: the timewalker is much weaker at the start, than further in the game, where it gains more and more health and takes much "time" to destroy!)