I finally caught the tube sheet leak at 3am and it was my own fault

So two nights ago I'm on the back side of a boiler job over in Gary, Indiana, and we get a call that the unit on the east line is losing pressure. Get up there and sure enough, water is weeping around a tube at the bottom row, not enough to flood anything but enough to show you a wet ring on the refractory. I grab my light and look close, and there it is, a hairline crack right at the weld toe maybe an inch long. The bad part is I rolled that row myself about four months back and I remember rushing the expansion because we were fighting a shift change. I told the lead it was ready when I should have run one more pass and let it cool slower. We cut the tube out, cleaned it up, and redid the joint with the preheat done right and nobody got hurt. So now I'm asking you guys, do you follow a set cool down time on small tube rolls or do you eyeball it based on how the metal looks? I keep going back and forth on what's actually safe.