Mob has spawn time of 90 hours with 10 hour variance. At 100 hours everyone will leave and come back for the (second) late window spawn (which was your initial concern).
You're just putting your initial problem off another 24 (48, 72, etc) hours and hoping people get tired of coming back for the repeated late windows. So now instead of only having one opportunity for a late window sock you're allowing for multiple ones, which I'm sure won't make the already uncooperative guilds more antsy and inclined to ensure they are the ones that get the mob after waiting at the altar a couple times.
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